Basic information regarding Biped rigging can be found on the VLE but this post should help you to get some more hands on experience if you are still struggling to pick up the techniques.
What is the Biped and how does it work?
Applying the biped to a model
The following video tutorials will comprehensively show you how to add a biped to your character model. If you do not have a character to work with then go ahead and download my 'Low Poly Man' from the list of tutorials here -> http://beorangedesign.com/tutorials/3D/
