The comma is the most popular kid in school. Everyone and anyone knows about it.
The comma we see at the end of a list is called an oxford, or serial, comma. The purpose of using an oxford comma is to avoid confusion, misunderstanding, and ambiguity.
Other times we omit it at the end of a list. Usually in newspapers, magazines and articles.
We use it to set off dates. Picasso was born on October 25, 1881, in case you were wondering.
If you use an introductory dependent clause, a comma separates the independent clause.
Sometimes a dependent clause intervenes, and if you want to use correct punctuation, place a comma before and after.
Here is a fun rule. Never use a comma before "that" and always use a comma before "which."
Why? A restrictive clause uses "that" to connect clauses, whereas a non-restrictive clause uses "which." Confused? Check out restrictive vs non-restrictive clauses in the grammar section.
Yes, always put a comma after introductory words, such as "yes," "no," and "or."
Use commas with adjectives if they can be separated by "and." It is a difficult, confusing, complicated rule. It really is a difficult and confusing and complicated rule. (See how it makes sense?)
Don't use commas if the adjectives can't be separated by "and." It's a valuable literary grammar rule. (You can't say "it's a valuable and literary and grammar rule. Nonsense.)
If you use a transition word, however, use a pair a commas. (However in this case is called a conjunctive adverb.)
Use a comma after "for example" and "that is" and "namely." For example, can you spot the comma?
I often use commas too. And I, too, get confused.
There is much, much, much more to commas. However, we covered a lot of the basics here. On to the next topic.