Acro and Rate are "similar as you can do some stunts in Rate. But with Rate your craft will go back to "level" flight.
Acro mode your craft "stays" in the position you last left its orientation in until it receives addition input from your transmitter. Acro is for full blown Racing and stunts.
Rate mode is for learning how to get ready for Acro mode. My advice, go straight to Acro and get your crashes over with. After Acro you will strongly dislike or even hate any other mode.