It's a long explanation to give, so here are two resources from blogs I like:
http://www.hyperarts.com/blog/tutorial-facebook-pages-with-static-fbml-application/
http://blog.webdistortion.com/2010/03/22/7-fbml-examples-to-rock-your-facebook-fan-page/
Also, check the FB developer section:
http://developers.facebook.com/docs/reference/fbml/
YouTube is surprisingly helpful for things like this, too.
Also, I super highly recommend lynda.com for professional grade tutorials for anything design / programming related. They really are superb.
I know a list of links isn't necessarily the most helpful thing for stuff like this, but I gotta tell you... get used to it for programming. You'll need to search answers like this over and over... at 3am...