Focus Attack

I’m trying really hard to understand the mechanics of this game. Obviously one of them is focus attacks. As a Sim player how and when do you use it. Currently I just use it to absorb projectiles to build my Ultra meter faster since I use Ultra 2. I’ve heard it can be used to anti-air but how exactly?

Focus backdash is a useful tool to get away from certain situations.

Also I take using focus attack in corner not a good idea due to slowness?

Thank you for responding. Now when I watch some more videos I can understand why they were using it.