The COLON is used to INTRODUCE SOMETHING.
The COLON can introduce a LONG QUOTATION, A LIST, SUMMARY, or IMPORTANT CONCLUSION.
** However, the COLON MUST come after an INDEPEDENT CLAUSE (or a complete sentence).
EXAMPLE
I bought several things at the grocery store: a banana, a box of fiber cereal, and a giant dried prune. (used to introduce a list)
** notice that there is an INDEPENDENT CLAUSE before the COLON
After watching the couple argue for two hours I came to one conclusion: neither of them knew what they were talking about. (used to introduce a conclusion)
** notice that there is an INDEPENDENT CLAUSE before the COLON
Here is a GREAT episode from GRAMMAR GIRL!
