As I am sure you know the rudder is a primary control.
In your early lessons you will have been shown that increasing power causes a pitch up and left roll/yaw, and reducing power right roll/yaw (with American engines)
Admitedly with the low power of he typical trainer the effect is not huge. You will probably first realise how significant it is when you try to climb on a constant heading, eg a navex, and wonder why your heading keeps drifting left,.or in the circuit doing touch and gos when you drift towards the left of the runway when applying full power, .....the reason, insufficent right rudder.
Unforunately the typical trainer often has the ailerons designed to reduce the need for rudder in turns to counter the adverse aileron yaw, so it is very easy to get lazy feet. Try to get the feel for the correct use of rudder as it will benefit you enormously