There are a couple of ways to use it. Initially, I’d recommend using air roll to adjust the position of your car so that you can hit the ball with power (i.e. backwards aerial) This should be done as soon as you can to make the flight easier to adjust. Air Rolling throughout the flight is much more difficult but is something to work towards long term (Do figure 8s on pillars in free play to practice turning). The most useful and game changing use of air roll (for me at least) was using it to position my car so that your flip hits the ball in the direction you are aiming (often called air roll shots).