This page explains how to properly use the colon [:]. Primarily, the colon is used to draw attention to the words that follow it, but it has other uses as well.
Use a colon after independent clauses to direct attention to a list of items or a quotation. Just make sure that the part of the sentence that precedes the colon is an independent clause (able to stand alone as a complete sentence).
My morning consists of the following routine: wake up at six, put on coffee, drink one cup, eat a bowl of cereal, take a shower, get dressed, and then head out the door.
Think about the words of J.F.K: “Ask not what your country can do for you; ask what you can do for your country.”
Use a colon between two independent clauses if the second sums up or further explains the first.
Life is like a box of chocolate: you never know what you are going to get.
Note: the second clause can begin with a lowercase or an uppercase letter.
If you are unsure whether to use a colon or a semicolon, ask yourself whether the first independent clause introduces the next, or if they are merely two connected ideas (in which case you would use a semicolon).
Use a colon after the salutation of a formal letter, to indicate hours and minutes, to show proportions, and between a title and its subtitle.
Dear Sir or Madam:
The ratio between girls and boys was 2:1.
Grammar Basics: The How To Guide to Grammar