Colons

Colon—Stylistic mark, never necessary, takes the place of a comma
USES:
1) Introduce a List.
Example: Bob excels in the following activities: wrecking his car while driving blindfolded; drinking bottles of hot sauce; watching football and scratching his ringworm foot bloody; and flunking English 060.
WARNING: A list must be introduced to use a colon. A similar sentence could be written: Bob excels in football, baseball and basketball. There is no introduction of a list and therefore a colon could not be used. It would be wrong to write: Bob excels in: football, baseball, and basketball.

2) After a statement that introduces a quotation.
Example: He began the meeting with this warning: “Gentlemen, Art Bell says the world will end in three years!”
We were at the pizza station when John shouted: “That girl is in my class.”

3) Many writers use the colon to define or expand on some object or subject within a sentence. Here is an example from Eudora Welty’s story “Powerhouse” (from Hot and Cool: Jazz Short Stories): “Powerhouse reads each one, studying with a secret face: that is the face which looks like a mask—anybody’s; there is a moment when he makes a decision.”

Here Welty is defining “secret face”. Another example from James Joyce’s “The Dead”: “So she had had that romance in her life: a man had died for her sake.” Here Joyce is defining