How to become a background singer?

I play the guitar and am going to move to nashville to pursue a career in being a guitarist. But i know that being able to sing back ground would greatly make me more wanted in a band. So im an ok singer, nothing special, but not awful either. How can i learn how to sing, or do i need to learn how to sing? Like do i need to know how to sing in the right key and stuff as a background singer or do i just sing close to the lead singer?