Okay, so people's grammar drives me crazy, so here are a few basic grammar rules to help you along. I have included examples and explanations.

Capitalization - Capitalize at the beginning of a new sentence, as well as all proper nouns. A proper noun is the name of a person or place. You also capitalize all "I"s when you are referring to yourself, such as "I'm" or "I've". You do not capitalize the cardinal directions unless they are in a name. Here are some examples:

"Today is Monday and I'm going to the south side of the city."

"I've never been to North Dakota."

Tenses - People get tenses wrong all the time. Tenses are:
Any one of the inflected forms in the conjugation of a verb that indicates the time, such as past, present, or future, as well as the continuance or completion of the action or state.

If you are writing a sentence, you have to make sure all of your tenses are correct. They all have to be either from the past, present, or future. Here are some examples of sentences done incorrectly:

"I wish people got it and find it as funny as I do."

This is incorrect because "got" is a different tense than "find" and "do." "Got" is past tense, while "find" and "do" are present tense. If you were to separate them into two different sentences, it would seem weird when you say it when it's incorrect. For example:

"I wish people got it. I wish people find it as funny as I do."

The sentence should be written as such:

"I wish people got it and found it as funny as I did."

or

"I wish people get it and find it as funny as I do."

Commas - Commas go when you would normally make a pause while speaking, or in between items on a list. Here are some examples:

"I've never had a steak, but I like hamburgers so I think I'd like it."

"I found a pencil, a pen, a stapler, and a hole punch."

Now, the comma between "stapler" and "and" is removable and not necessary. You can use a comma before the "and" or not, either way works.

Semicolons - A semicolon is used whenever you have two sentences connected and the conjunction is left out. Conjunctions are words like "and," "or," "but," "yet," "for," "nor," and "so." Here are some examples:

"Finding time to do all those things is hard; the time just doesn't exist in the day."

That sentence could also be written as such:

"Finding time to do all those things is hard, for the time just doesn't exist in the day."

Parentheses - Parentheses are used when you're enclosing words that clarify or are meant to be set aside. A period is put in the parentheses only if there is a full sentence within the parentheses. Here are some examples:

"He told me that it was awesome (which if I find kind of funny)."

"It's really warm outside and I like it. (Though I think it's really too humid out.)"
or
"It's really warm outside and I like it (Though I think it's really too humid out.)."

Quotes - Quotes go around a sentence if it is what someone has said directly, or if you're referring to a word or phrase as it is outside of a sentence, or the context. You can see examples of the latter thing I said throughout this entry. I'm going to break the format here a little bit, just so you can see a proper example of the first thing I said about quotes. Here is quotes used correctly:

He said, "I had ten chickens, but two died."

Punctuation ALWAYS goes inside of the quotes. Here's another example:

I ran to the store and when he talking about it he said "You're really fast," but I disagree with him.

If you have quotes inside quotes, you would use the single quote. Here's me going back to the format that's correct:

"He said, 'I love cheese.'"

"I've been to the store."
"I've" is a combination of "I" and "have."

"I haven't been to the store."
"Haven't" is a combination of "have" and "not."

Basically, you place the single quote wherever you've taken out a letter. Contractions can be used more than once in one word. For example:

"I couldn't've seen that coming."
That is a combination of "could," "not," and "have."

Your, you're distinction - You use the word "your" when you're talking about possession, and "you're" when you want to say "you are." Here are some examples:

"You're an evil person."

and

"Your friend is an evil person."

There, their, they're distinction - You use the word "there" when you're talking about a place, "their" when you're talking about possession, and "they're" when you want to say "they are." Here are some examples:

"I see what you did there."

"They're awesome people."

"Their friends are visiting them."

Then, than distinction - You use the word "then" when you're talking about time, and "than" when you're comparing something.