How does the robo auto-tune app work?

OK so i finally got a mini mic for my iPod touch and i get: I am T-Pain but every time i save one it doesn't play so i got robotune and it always says plug your mic in so i do that and say what i want to say but i don't know how you listen to it i tried touching the music button but it didn't work! Help please I've been looking forward to auto tune apps for a while!