lol redhair
Well, what it basically is, is just a way to locate web/ftp sites around the world so people in different areas in the world can have access to a closer server, which makes for a quicker download.
So if you have files, or a webpage you want to mirror, find someone with hosting or their own server in a particular country, or area of a country (eg. USA east and USA west); then send them all the files required to run the site.
The biggest challenge in a mirror system is to have dynamic content that is identical on all pages, and also keep ftp servers updated with all the latest downloads. But it's all part of the job, and a good challenge.
