Use a Comma to:

Connect two independent clauses  

with a coordinating conjunction: for, and, nor, but, or, yet, so.

  • He wanted to watch his sister play soccer, but his girlfriend insisted on going to the movie instead.

Follow introductory words and phrases at the beginning of a sentence 

Introductory words include moreover, therefore, thus, yes, no, well, please, however, still, yet, oh.

  • However, when she got there she wasn’t hungry.

Introductory Phrases include:

An infinitive phrase:

  • To get where he was going, Frank had to walk the long way around.

A prepositional phrase of more than four words:

  • Through the walls of her bedroom, she could hear her parents quarreling.

Follow a dependent or subordinate clause that comes at the beginning of a sentence

  • Because she scored very high on her SAT, Jennifer was admitted to five top-ranked schools.

Separate items in a list of words, phrases or clauses

when there are no commas within the listed items.  

  • He decided that he would write a resume, fill out a job application, and submit it to the pizza parlor before the end of the day.

Separate coordinate adjectives that describe the same noun   

  •  She wore a green, flowing gown to the dance. (Both “green” and “flowing” modify the noun “gown.”)