Appositives are nouns or noun phrases that represent the same thing and sit next to each other in a sentence. For example,
My wife, Jenny, should know how lucky she is to be married to me.
Here, My wife and Jenny are the same person; Jenny serves to explain my wife.
Apposition is a technical concept. In fact, [...]

Here are some common comma mistakes to avoid.

Setting off the subject from the predicate.
Jennifer and I, went to the store.
Adding only one comma of a pair.
The doctor, who was a gentleman left the room while I disrobed.
Not setting off non-essential clauses.
Doctor Who which is a long-running British T.V. series is undergoing a leadership [...]

Since the dawn of time, man has waged war because of deeply held beliefs. But none of these beliefs have been so divisive, so enraging, so trivial as the Oxford comma.

Problem:

Every time you set your pen to paper, some testy copy editor runs over and writes “comma splice” all over your work.
Solution:

Learn to use the comma.