Comments in CSS are the same as multi-line comments in C programming. They begin with /* and end with */. For example, you might want to begin a style sheet with basic information about the creator of it, how to contact him if you have questions, his web site if he has one etc. Below is how such information could be commented.
/*-------------------
author: Sam O'Brien
email: sam@sample.com
web site: StylesBySam.com
------------------------*/
The only purpose of the dashes is to block off the comments. Remember, everything inside the opening and closing marks is part of the comment and will in no way affect your code. You can use comments to make notes to yourself and to designate where code that styles specific sections of your page begins and ends.