Words, phrases, and clauses joined in a series are separated by commas.

• Men, women, and children crowded aboard the train.
  
• Her job required her to pack quickly, to travel often, and to have no personal life.
  
• He responded patiently while reporters shouted questions, flashbulbs popped, and the crowd pushed closer.
  

When the last two items in a series are joined by a conjunction, the final comma is often omitted, especially where this would not result in ambiguity. In individual publications, the final comma is usually consistently used, consistently omitted, or used only where a given sentence would otherwise be ambiguous or hard to read. It is consistently used in most nonfiction books; elsewhere it tends to be used or generally omitted equally often.

• We are looking for a house with a big yard, a view of the harbor[,] and beach and docking privileges.

A comma is not generally used to separate items in a series all of which are joined with conjunctions.

• I don't understand what this policy covers or doesn't cover or only partially covers.
• They left behind the fogs and the wood storks and the lonesome soughing of the wind.
  

When the elements in a series are long or complex or consist of clauses that themselves contain commas, the elements are usually separated by semicolons, not commas.