Colons and semicolons are two types of punctuation. Colons (:) are used in sentences to introduce that something follows like a quotation, example or a list. Semicolons (;) are used to join two independent clauses, to separate main clauses joined by a conjunctive adverb or to separate items in a list that already uses commas. Still confused?
Check out the YourDictionary Punctuation Jungle infographic on punctuation for an easy-to-understand visual explanation.
For more information on how to use colons and the six key rules for colon usage, check out the YourDictionary article entitled Grammar Colon Usage. For information on using semicolons, colons and commas, check out the usage tips given in What Are the Fourteen Punctuation Marks in English Grammar?