What are the legalities regarding this scenario involving lyrics?

i wrote some really good lyrics, but im having trouble writing the music for them! i was going to ask someone on y!a if they would be willing to sin g the lyrics and then post them ou youtube. once i finished the music for the song, i was going to send the completed song to a well known band to see if they would publish it (i know its a long shot ). then i got to thinking about the legalities of this scenario! for instance, would anyone listening to the video on youtube be able to steal the song? or the person singing it? and since the singer partly contributed to the song, would i have to get their permission to use what they sang? would i have to get their permission if i were to send the song off to a band? what are all of the legalities of this situation? answers would be so much appreciated! thank you so much for your time!