If you are being hit by your opponent's attacks and you are in midair, you can perform an Aerial Roll. It is possible to control the direction of where you roll. You will not be able to move for a certain amount of time while you're perforiming an Aerial Roll, but you'll also become temporarily invincible during the Aerial Roll. When being hit by an opponent, there is a period of time where the Aerial Roll is not available and inputting the Aerial Roll command during this time will not do anything.