Oh so easy to use--oh so often misused. A colon comes after a complete sentence and before a list. So, it's a pretty easy pattern to learn.

Complete Sentence: list item, list item, and list item.

I need to go to the store to buy several items: milk, eggs, and bread
In English class we read about a number of heroes: Odysseus, Joseph, Sir Gawain, and Gilgamesh.
When I was caught in the rain, I soaked all my clothes: my pants, my hat, my shoes, and even my socks.

You need to make sure that you don't make a few common mistakes.

1. Make sure that you have a complete sentence before the colon.

Wrong
Cari wants to learn several new sports including: basketball, baseball, soccer, and volleyball.

The part before the sentence is NOT a complete sentence. After all, you can't just say "Cari wants to learn several new sports including."

Correct
Cari wants to learn several new sports: basketball, baseball, soccer, and volleyball.

The colon connects the series to the complete sentence "Cari wants to learn several new sports."

2. Make sure that the list describes the last word or phrase in the sentence.

If you look at the samples, milk, eggs, and bread are types of items; Odysseus, Joseph, Gawain, and Gilgamesh are types of heroes; and pants, hat, shoes, and socks are types of clothes.

Wrong

The keyboard, mouse, and wires do not describe the floor, so the sentence isn't constructed correctly. Since these are obviously part of the computer, we must get "computer" into the end of the sentence.

Correct

Yep, the list items correctly describe the last word / phrase in the sentence, so this is a correct use of a colon.

The charter review committee now includes the following people, the mayor, the chief of police, the fire chief, and the chair of the town council.

Her recipe for gunpowder included: saltpeter, dry oatmeal, and ground-up charcoal.

I want an assistant who can: input data, write reports, and complete tax forms.

There are many exotic fruits I have never eaten mangosteens, durians, longans, and rambutans.

Literacy Education: A range of colon rules
University of Ottawa colon rules