What is a cache, how do I get them and why do I have to clean them up?

A cache (pronounced CASH) is a place to store something temporarily. The files you automatically request by looking at a Web page are stored on your hard disk in a cache subdirectory under the directory for your browser. So you get them by visiting any web page, and you clean them up so you can clear room on your hard drive.

I use onyx to clean them. Is this something u recommend?

I don’t bother with it. My Mac has only been turned off for about thirty minutes in the last two years. Don’t turn your computer off and Cron will take care of things.

Or you can run all the maintenance scripts by running:

sudo periodic daily weekly monthly

from the Terminal.

I wouldn’t really worry about unless you are having problems.