Unlike PHP and JavaScript though, CSS comments can only be used one way.

Begin your comment with a /*, and end it with */. As an example:
/* Hey, this is a comment */

The comment block can span multiple lines:
/*
Howdy there,
partner
*/

How you lay your comments out is down to personal preference. I usually do the following:
/*
* This is my multi-lined
* comment. I have all
* asterixes lines up with
* two spaces after before
* starting the text.
*/

It make it much easier to pick out comments away from large chunks of code this way.