IPhone ring tone question?

I tried looking up old posts to see if there was an answer and I didn’t find it. I am a PC user. I paid for a ringtone on itunes but it downloaded to my song list. I can’t figure out how to move it to my ring tone so I can use it. I know, I should probably be googling or something, but I feel like I need to ask a friend who know something about iPhones and well, you guys are my friends.