Every word in our language can be categorized as a part of speech. There are eight of them: noun, verb, pronoun, adjective, adverb, preposition, conjunction and interjection. A noun is a thing. It can be something concrete, like a person or a car, or it can be an abstract, like love. A verb is an action. It describes something being done. A pronoun takes the place of a noun. He, she, I, me and we are all pronouns. Adjectives modify nouns by adding a descriptive word to the noun that add some detail to the noun. Adverbs modify verbs in the same way. Prepositions show relationships between two objects. He moved across the bridge. The preposition is across, which shows the relationship between the subject and the object of the sentence. Conjunctions are words like "and," "or" and "but." They connect two or more things in a sentence. An interjection, which some educators ignore when discussing the parts of speech, include words like wow. Just about anything you can follow with an exclamation point is an interjection, and although there are no strict rules governing them, it's a good idea to limit their use.
Simple sentences must contain a subject and a predicate that expresses a complete thought. A subject is the person or thing the sentence is about. The predicate is the part of the sentence that tells us what the subject does. "Joe went home" is a simple sentence. Joe is the subject. The verb "went" and the noun "home" form the predicate of the sentence. The subject of the sentence did something. Sentences get more complex than this, but there are always clear subjects and predicates. When you swap the order of these elements, you create passive writing, which you should try to avoid as much as possible. Here's an example of passive writing: "The car was hit by Joe." This puts the focus on the car, which should be the object of the sentence and in the predicate. To make this sentence active, you would write, "Joe hit the car." The only time you might write passively is if you want to keep the identity of the subject a secret. "Joe was hit on the back of the head" is passive, but it would be acceptable if you didn't know who hit Joe on the back of the head, or if you wanted to keep it a secret.
There are many rules about punctuation and how to use it. Periods are generally understood. A period means the end of a sentence. One confusion about the use of periods is when they are used in abbreviations. If the abbreviation is pronounced letter by letter, such as USA, periods aren't needed. Question marks, again, are usually understood. Use them when something is being asked. Exclamation points belong with interjections and should be used sparingly. Use commas to separate complete thoughts, to separate a series of things or to introduce dialogue. Commas can also be used to set off introductory phrases and words or phrases incidental to a sentence. Colons are used to introduce lists, and a semicolon is used to join independent clauses. It replaces a period between the clauses. If you use a semicolon in this way, do not use a capital for the sentence that comes after the semicolon.