our simple words help to explain the use of commas:

before, after, within, and around.

Here are four basic rules for the use of commas:

A comma is placed before a conjunction (and, but, yet, or, nor, for, so) that joins two complete sentences (independent clauses). For example,

I wrote my last paper gradually, and this process was successful.

A comma is placed after an introductory phrase or clause. For example,

After writing all night, I wasn't sure if my paper made any sense.

Commas are placed within a series of items. For example,

I like to start composing with brainstorming, mapping, and fastwriting.

Commas are placed around a nonessential phrase or clause. For example,

Procrastination, which too many students still practice, usually leads to anxiety and frustration.

For a more detailed and more formal explanation, see The New Century Handbook or a similar source.