before commas...

an independent clause is the main part of your sentence. it includes a complete subject and a complete verb.

The telephone rang.

(subject) (verb)

before commas...

a dependent clause is called a subordinate clause. it contains a subject and verb, but cannot stand alone as a sentence because it contains a subordinating conjunction

before commas...

a subordinating conjunction can answer one of these questions:

how, why, when, under what circumstances?

Because it was loud, I jumped when the telephone rang.

commas

use a comma to separate independent clauses joined by the coordinating conjunctions and, but, for, nor, or, neither, yet

You understand the use of commas, and your instructor is overjoyed.

commas

use a comma to set off an introductory dependent clause

If you had not gone, the plan would have been successful.

commas

use commas to separate words, phrases, or clauses in a series

She looked behind the door, under the table, and beneath the chair.

commas

use commas to separate non-restrictive clauses and phrases from the remainder of the sentence

The Queen Mary, which is a large boat, was built in Scotland.

commas

use commas to separate parenthetical words, phrases, or clauses

You are, however, correct in your statement.

commas

use commas between coordinating adjectives

She was pretty, nice, and funny.

commas

use commas to separate dates, places, initials, or titles/names

John left on July 6, 1998, to go to Chicago.

Rosa Gonzales, MD, was the principle witness for the defense.

commas

use commas to separate a short quotation

Jillian asked, “Are you ready?”