English is a very confusing language. Its grammar makes it harder than most. Seeing as I want to become a copy editor one day, I figured I could give you all a brief lesson.
To, Too and Two
"To" is used when you are indicating a person, place or thing. "Too" is used when you are saying something is "in addition". "Two" is a number.
ex. Are you going to work?
ex. Too bad you couldn't come.
ex. Those two are up to no good.
There, Their and They're
"There" is used when you are indicating a place. "Their" is used when you are saying someone possesses something. "They're" is a conjunction word meaning "they are".
ex. She's over there.
ex. Their house is huge.
ex. They're having a party.
When a sentence is indicating a he/she/I, you use "who". When a sentence indicates him/her/me, you use "whom".
ex. Who is going? (unidentified he/she)
ex. Whom did you hit? (unidentified him/her)
When to Use a Comma
There are independent and dependent clauses in sentences. A prepositional phrase is a dependent clause. This means the phrase cannot stand on its own. Therefore, it requires a comma.
ex. After the fire, no one knew what to do. (Notice how "after the fire" isn't a full sentence, but "no one knew what to do" is.)
Another situation in which you use a comma is if you have two independent clauses. We call this a compound sentence. "And" and "but" are the most common coordinating conjunctions.
ex. She knew she had no chance, but she did it anyway.
You also use commas in lists. (Lists have three or more terms.) However, depending on how you prefer to write, you can use the Oxford comma. This means you use a comma between everything listed. If you choose not to use the Oxford comma, then you don't put a comma at the end between the two final words.
ex. (with Oxford comma) I need to work out, go shop, and do my homework.
ex. (without) My favorite foods are chicken, pasta and chocolate.
There it is folks. A short grammar lesson by me. I hope you learned something.