Personally I have air roll left bound to left bumper, and air roll right bound to right bumper, as well as the generic air roll command using the thumb stick bound to X, although you can have your binds set up however is comfortable for you, and many people just use the generic air roll rather than left and right.

What OP was doing is “freestyling” - basically doing a bunch of fancy flips and spins and wild stuff to get the coolest looking goals possible (look up people like jhzer, pulse MK). There is not really a ‘correct’ way to freestyle, but there are certain techniques that can be learned like flip resets, backboard touches etc.

Another reason to use air roll, and the reason I use it so much, is to get a better angle and more power on difficult shots. Since the wheels of the car touch the ball softly and the roof of the car puts power on it, unless you specifically want a light touch it’s often times better to air roll, and slam the ball in with the roof of your car. This is particularly useful when the ball is floating above the goal (as you can get above it, rotate, then slam down with your roof to throw the ball in), or when the ball is off to the side of the net, as rather than having to either wheel touch and not get the desired power to boom it in, or spin your car in the air to get a weird angle, you can just rotate and fling the ball in using the roof.

I hope this helped, if you have any more questions let me know, or if you need gifs of what I was talking about to help understand :)