A colon (:) is a fairly common punctuation mark with a varied number of uses. It can be used to introduce a quotation, an example, a series, or even an explanation. Secondly, it can be used to separate two independent clauses. Finally, a colon can be used to show emphasis.

Examples:

• You have two choices: finish the work today or lose the contract.
• That’s because we have one goal: for you to consider your website a success.
• John has all the ingredients: minced clams, milk, potatoes, and onions.