There are three main uses of the colon:
between two main clauses in cases where the second clause explains or follows from the first:
That is the secret of my extraordinary life: always do the unexpected.
It wasn’t easy: to begin with, I had to find the right house.
to introduce a list:
The price includes the following: travel to London, flight to Venice, hotel accommodations, and excursions.
The job calls for skills in the following areas: proofing, editing, and database administration.
before a quotation, and sometimes before direct speech:
The headline read: "Taxi Driver Battles Gangsters."
They shouted: "Our families are starving! We need land!"