A colon is a punctuation mark. It looks like this :
A colon is often used at the beginning of a bullet pointed list.
- kiwi fruit
It can also be used in some other types of list, but not all lists.
The first of the following sentences needs a colon, but the second does not.
These are the people I am inviting to my party: Kate, Joe, Adil, Dwayne and Jamila.
I am inviting Kate, Joe, Adil, Dwayne and Jamila to my party.
So how can we decide whether we need a colon or not?
If the section of the sentence before the colon makes sense on its own, then we use a colon. If it doesn't make sense on its own, we don't use a colon.
'These are the people I am inviting to my party' makes sense on its own, but 'I am inviting' does not.