Colons are most commonly used to indicate a forthcoming list, but you also will find them throughout sentences and business communications. Learning the proper usage for colons will make your writing look more professional.
Insert a colon after a complete sentence to indicate the start of a list. For example, "We need several things from the market: bread, milk, cereal, strawberries and lemons."
Replace a semicolon with a colon between two strong clauses when the second clause illustrates or explains the first clause. You would write, "Garlic is my favorite spice: it brings out the flavor in my best Italian dishes." It is not necessary to capitalize the first word of the second clause.
Use a colon to introduce a quotation of three or more lines. The quotation should be indented an additional 1/2 inch on the right and the left.
Put a colon after the salutation (greeting) of a business letter. Write "Dear Mr. Jones:" or "Dear Human Resources:" The use of a comma after a salutation indicates a friendly letter, so it is not acceptable to use this form even if you are acquainted with the recipient of your business correspondence.