Use a colon to bring attention to something that follows.
Use a colon after a complete though to introduce something that follows.
Use a colon before a list of items.
A colon is similar to a semi colon, but it does not have a comma on the bottom.
Use a colon afters words such as: The following, such as, as follows, and as the following manner.
Please arrive with the following: a computer, a pencil, and a willingness to work.
I went to the doctor; he told me that I have the flu.
Semi-Colon usage instructional video.