Colons (:) have three uses.

They are used to introduce a list:

  • We can see many things in the sky at night: the moon, the stars, the planets, comets and even planes.
  • Please check the following:
    1. the bedding
    2. the towels
    3. the kitchen utensils
    4. the pots and pans

They are used to introduce a single item, when you want to emphasise that item:

  • There is one thing that he will not accept: stupidity.
  • We forgot to ask the most important question: who is buying lunch?

They are used to show the time:

  • The meeting starts at 8:15pm.
  • 09:00
  • 21:00