Colons (:) are used in sentences to show that something is following, like a quotation, example, or list. Semicolons (;) are used to join two independent clauses, or two complete thoughts that could stand alone as complete sentences.

Mallick gave a good answer. You can also use semi-colons to separate items in a list when the individual items also use commas (,). For example: "Among the guests at the party were Elizabeth II, Queen of England; Harald V, King of Norway; and Mr Bean, a famous comic character."