Colon :
A colon introduces the information that comes after it. It tells the reader that something is coming.

Examples
I’ve narrowed my choices down to two schools: Indiana or Michigan State.
As I see it, you’ve committed three criminal acts: fraud, perjury, and misrepresentation of financial assets.
I’ll say this for him: he’s honest even if it’s difficult.

Semicolon ;
The semicolon connects two complete sentences that are related.

Examples
Franklin D. Roosevelt was the U.S. president for four terms; he led the country through World War II.
Roses are red; violets are purple.
I’m ready to go; I hope you’ll be ready soon!