A CSS compressor is a program that minimizes a CSS style sheet by removing all extra white space. It may also do additional things to make the style sheet smaller. The purpose of a CSS compressor is to make the file size smaller so that it downloads more quickly. You should use one to compress your style sheets. There are many available for free on the web.
There is a simple web-based CSS compressor at http://www.cssdrive.com/index.php/main/csscompressor.
Here is another excellent free compressor at http://csscompressor.com/.