Use a colon to introduce an idea, list or quotation. The clause before the colon must be a full sentence. If not, do not use a colon.
Use the colon to introduce an idea that is an explanation or continuation of the one before the colon.
There is one thing you need to know about statistics: they are fascinating.
Start the explanation or continuation with a capital letter if it is a formal quote that is a full sentence, or more than one sentence.
There is one thing you need to know about statistics: They are fascinating and I do not know why anyone would think differently. Truly they have made my life better.
There is one thing you need to know about statistics: “A better thing has never been created,” said the Chief Statistician.
Use a colon to introduce a list.
The statistics incorporate varied data: housing, schooling and population information.
The statistics incorporate: housing, schooling and population information.
Use a colon to introduce a quotation. The quotation should begin with a capital letter.
The judge stated: “You have suffered.”