Format
As mentioned, at the start of the show, the band plays a song and the host "randomly" gives audience members a chance to sing part of the song. If they sing it correctly, they become one of the contestants on the show. This part of the show is actually staged, and the contestants are preselected. During this part of the program, you can sometimes see (as the contestants run up to the stage) that the lyrics for the song are being scrolled on a banner over the stage so that the preselected contestants don't make a mistake.
Read more about this topic: The Singing Bee (U.S. Game Show)