Yes, use the rudder to coordinate your turns. Most trainers have some adverse yaw (actually most planes in general do) which means the nose will point away from the direction of the turn while you are applying aileron. You can use aileron differential to get rid of a lot of that, but you still need rudder to make the turn smooth and coordinated. Think of the aileron as the coarse control for turning- it gets you going in the right direction. And think of the rudder as the fine control- it lets you adjust how tight the turn is and balance the forces acting on the plane. The rudder should be your primary directional control, especially for adjusting your heading. Start using it as early as possible and you will save yourself a lot of headaches.