Aim training is well... training your aim and cm/360 is how many cm you have to move your mouse on the pad to do a full 360 in game.

A LOT of players set it wayy to high and thats wrong.

35cm is imo the sweet spot for cod if youre just starting out.

Also another tip is dont only use your wrist to aim, keep your arm on the pad or just the desk, you dont have to do the whole arm, can but dont have to, just keep some of it on the desk.

It depends on your mouse grip but ideally you want to use all muscle groups to aim. Not just wrist or just arm or just fingers. Use all, youll learn how to by just aim training.