Listen: I can help you.
Take note, however: I ain't no grammar Nazi. Whatever those guys tell you, words and sentences are clay, meant to be manipulated to your liking. Sometimes sentences aren't complete, and it's perfectly okay. Like this one. The #1 rule is: If the reader understands what you're saying, then your words are working. Writing well means writing so that whoever's reading can hear you. It's the egotistical modern mind that makes you think everyone knows the voice in your head. They don't. You can get that voice across on the page or screen by knowing how to manipulate language and the punctuation that accompanies it. As they say, you've gotta know the rules to break them.
First, you need to know what a complete sentence is (in the grammar world, these are called independent clauses). A complete sentence is like a flower. A flower has two main parts: the bloom and the stem (lay off, I'm no floriculturist), and there are two main parts in a simple sentence: the subject and the predicate. Take away one or the other, and all you've got left is a fragment. Or, in the case of the flower, you're left with just a stem or just a bloom--both interesting but neither a whole. At the same time, every flower is made up of individual plant cells playing all sorts of roles to create seemingly endless varieties of flowers. In sentences, those cells, those individual building blocks--they're words. And they all have different roles to play in the sentence. (Not a great metaphor, but you get what I'm saying.)
You may be thinking, subject and predicate? What the heck does that mean? The subject in a sentence is who/what the sentence is about. If I say, "The dog ran," you know the sentence is about the dog. The predicate is...up for debate...but basically, it's the part of the sentence where you find an action in reference to the subject. In, "The dog ran," the action word is obvious: ran.
Now think about this line: "The man has a." The man is obviously who the line is about, and the action is 'has', but you're left wondering what he has. So there's one thing the predicate must do as well as hold the action word; it must complete the thought. In other words, it must answer that unspoken question in the reader's mind that has now been built by the subject and the action: "The man has a...WHAT?!" In this case, I can tell you the man has a brand new steampunk pipe to add to his Dragon Con cosplay. You'd never know that from the fragment I gave you to start with.
So sentences are made of two parts, a subject and predicate. The subject is the who/what the sentence is about, and the predicate holds an action in reference to the subject and helps complete the thought. Now what about all the other words in the sentence?
Remember, they're all building blocks. Every word in a sentence performs a specific job. Most play supporting roles by describing things, connecting things, adding things, or introducing things, while some play the lead roles. There are 8 roles words can play (this is up for debate too), and some words can switch roles depending on what they're doing in the sentence. The 8 are called parts of speech. Click here to see a description of each, but we'll go through most of them below.
Let's work through this sentence as an example:
Harry Potter is a young and confused boy at the beginning of his story.
First let's figure out if that's a complete sentence. Who or what is the sentence about? Harry Potter. Incidentally, Harry Potter is a noun (a person, place, thing, or idea). But don't get yourself thinking you should always look for a noun as the subject. For example, look at this sentence: That he loved her was not enough. There, an entire phrase is the subject: That he loved her. When you look for the subject, don't look for a noun. Instead, ask yourself, "Who or what is this sentence about? Who or what is the action in reference to?"
So we've got our subject, Harry Potter, which happens to be a noun. Now we need action and for the thought to be complete. Action words are called verbs. In our sentence, the verb is the word is. This is one of the many maddening aspects of language, especially English, because is refers to a 'state of being.' Sometimes we skip over is when we look for an obvious action word. We're hoping to see bludgeon or cross-dress or decorate. We can picture those things and know they involve actual movement. But is, was, has been, will be--that kind of stuff is existential and abstract. Alas, 'states of being' are still verbs, and that's what we've got in our sentence about Harry.
Right, so we've got the subject (Harry Potter) and the action (is). To complete the sentence, we have to complete the thought. Harry Potter is...WHAT? This sentence is more complex than 'The dog ran,' so you've got to do some work. You must strip away everything extra in the sentence and get right down to the basics. Here, the very basic answer is: a boy. Harry Potter is a boy. That's the answer to our question; that's the meat of our sentence; that's an independent clause that can stand alone without any other information.
Our independent clause is: Harry Potter is a boy.
EVERYTHING ELSE IS EXTRA.
To begin, let's deal with a. (Remember: a appeared in the answer to our question.) A is an article. There are three articles in English: a, an, and the. Their job is to introduce nouns. Lots of languages have these. Like in German, you use der, die, and das. Unlike in German, our articles don't indicate the gender of the noun. Instead, they indicate whether the noun is something specific or something general. You might have heard the articles being referred to as definite or indefinite. All that means is like if I said, "That's the dress I want," you'd know I meant a specific or definite dress, but if I said, "I need to find a dress," you'd know I didn't have a specific one in mind, or was indefinite about what I wanted. These appear throughout your writing all the time, and you use them in speech without even thinking about it, unless English is your second language. Then you often forget to put articles in or don't quite know how. That's part of the beauty of so-called 'broken' English and what sometimes gives it a common diction: "I walked to store to buy bread, and store owner gave me free candy bar." See? The message is there but the articles are missing. Can you find the other article in our sentence about Harry?
Next is the word young. In this sentence, young does the job of describing the noun boy. There are two types of descriptive words in English: adjectives and adverbs. Though they're a bit more complicated than this, usually adverbs describe verbs, such as quickly running or beautifully dancing, and adjectives describe nouns, such as the angry magician or the freckled forehead. In our sentence, young describes boy. Since boy is a noun, young is an adjective. Look closely and you'll see another word describing boy.
Next is the word and. And is a conjunction. Conjunction is a fancy word for bridge. It's a connecty word. Often conjunctions join two complete sentences. (Ron uses bad language, but he does so with good comedic timing, so we don't mind it, for bad language used with good timing can be really funny, and this aspect of his personality contrasts perfectly with Hermoine's perfectionism.) There are 7 conjunctions total: for, and, nor, but, or, yet, so. You may have memorized the mnemonic FANBOYS in elementary school to help you remember those.
The words at and of in our sentence are called prepositions. Often, when you can't quite work out what a word's job is, it's a preposition. I have to look them up in the dictionary all the time. A trick to recognizing them is knowing that they indicate where something is in space. Picture one of those big Southern Colonial houses. Now picture a black cat sitting on its embroidered pillow. Now it's in the arms of its owner on the second-level porch. Now kitty is under the sprawling live oak that's draped with Spanish moss and happens to be beside a small child who is playing within a tent. Get it? Those are prepositions and usually indicate where something is in space. Usually.
The word beginning in our sentence is another noun. Beginning can also be an adjective (remember, that's a word that describes a noun). If the sentence said that Harry was a beginning guitar player, beginning would be describing what kind of guitar player he is and would therefore be an adjective. Here, it's a noun. This is where people often get confused. They think, "Wait, a noun?! We already have a subject!" Remember: Nouns aren't always subjects, and subjects aren't always nouns. Sometimes nouns are just in with those bits of extra information about the main sentence.
There's something you should know now that's gonna take you to the next level. It's a super tricky thing called the prepositional phrase. Prepositional phrases contain a lot of that extra info I've been talking about. They're called prepositional phrases because they start with a preposition. The reason these trick you is because lots of times they include a noun and can look like mini sentences themselves, making you think you've got a complete sentence when you really don't. In our sentence, we've got 2 prepositional phrases: at the beginning and of the story. The key is knowing your prepositions. If you know that at and of are prepositions, you'll get that warning light in your head saying, "Hold up--there's a prepositional phrase! I should be able to remove it and still have the meat of my sentence left."
Recap: Harry Potter is a boy. That's the meat. The extra stuff: young and confused describe what kind of boy, and at the beginning and of his story are prepositional phrases containing extra info about the meat. We're almost done.
The only thing left to identify is that little word his that's sitting in our second prepositional phrase. His is a pronoun (technically a possessive pronoun since it's showing ownership). Pronouns are words that take the place of nouns. It's nice to have those, otherwise we'd be stuck saying things like, "Harry is great. Harry is the best Quidditch player ever. Harry's scar is so awesome. Harry is my hero." Instead, we can use pronouns like he and his once in a while so we don't sound like robots.
That said, most sentences are more complex than the one we've dissected and include more than one independent clause, which means more than one subject and predicate.
For example, a beautifully complex sentence:
"I know the night is not the same as the day: that all things are different, that the things of the night cannot be explained in the day, because they do not then exist, and the night can be a dreadful time for lonely people once their loneliness has started." - Hemingway in A Farewell to Arms
As a last tip, remember that the first word of every sentence should start with a capital letter, even if you're being creative. Unless it's in a poem, then--well that's definitely a separate lesson and one I wouldn't dare try to teach. Just trust me: Start your sentences with capital letters and end them with the correct punctuation. If you're saying something exclamatory, use an exclamation point! If you're asking a question, use one of these ? at the end. For all the rest, use a period.
Oh! Don't forget one of the best and most underused parts of speech: the interjection. Interjections are exclamations. I'll let Batman show you some of the more awesome examples that exist.
So now you know the basics. You're that much closer to getting that raise due to the fabulous email you'll write your boss, confidently helping your daughter with her English homework, and writing grammatically beautiful love letters to your favorite boys.
Next up, connecting sentences the right way! Death of the run-on for good! Banishment of the unclever fragment! Power to the complex, compound, and compound-complex sentence! I can feel your excitement through the screen. :)
(DISCLAIMER: Hey, hey, I know it's all a lot more complicated than this, but this'll get you started and rolling! Good luck!)