How the helll do I set up my new ring tones on my iphone 3????!!?

OK, so I pressed the button that says "Buy more tones" it takes me to the website, I purchase a Casting Crowns song, and is it in the ringtones list?? NO!!!!!!!! HOW in the hell do I set this up??? Its on my iphone, but I cant figure out how to make it a ring tone OMGOSH I HATE ELECTRONICS!!! I cant take this crap anymore why cant it be simple PLEASE help me with this I just want my ringer to be the song I just purchased