Operation of a radius server

I was just hoping someone here could explain to me how the radius server process works. My situation will be authorizing for DSL. I think the process is: My DSL wholesaler gets requests for a logins under my realm to their NAS, then sends it to me, then I send back a yes or no answer. My question is what information do I have to supply to my DSL wholesaler and what information do I need from them? regarding authorization types or encryption? Any info would help a lot. Thanks