Punctuation - the colon

The function of the colon is:

• To signal the special relationship between the parts before, and the parts after it. (Every man and woman has three aims: to live, to love, to learn.)
• To introduce a list. (I have mailed to you the following items: copy of cash book to year end, cheque butts, and deposit slips.)
• For the introuction of a formal or long quotation with such words as reads or read and writes or write. (Graeme Kinross-Smith, in his "Writer: A Working Guide for New Writers, writes of Virginia Wolf: "[She] expressed, more cogently than Richardson or Joyce perhaps, the ideas that led to the new way of looking at the world in fiction.") Note that a colon is also used before the subtitle of a book, as above.
• The colon is also used to: separate information, as in chapter and verse (John 3:16); act and scene (King Lear, Act Three: Scene Two); hour and minute (8:20 a.m.); volume and page reference (World Book, 8:320).

There are more but too many to list here. Every writer should have a good book on punctuation on their bookshelf so make this a priority for your reference library.