All you need to do is talk, and Autorap does the rest! You can change the backing track, but only a few limited free options. It's a great way to start and ensure everyone experiences success before moving on to other apps.
Talk mode: instantly turn your words in to a rap song
Rap mode: Auto-tune your freestyle verses (corrects bad rapping)
Remix - recreate the rap in different beats
Rap Battles - show off your rapping.