Not all full scale aircraft use rudder in turns....the 727 doesn't and when I was in the 777 sim I was told to leave rudder alone and was able to turn using just ailerons.....
You control an aircraft in 3 axis....pitch (elevators), Roll (ailerons), and Yaw (rudder)...yaw is the side to side movement of the nose......
When to use rudder....kicking out the crab doing a crosswind landing, helping in turns if the wind is strong......even doing a loop to keep the airplanes heading straight.....almost all aerobatics require the rudder some what.......
The best place I've found to learn rudder is pratice a flat turn, where you add rudder and opposite aileron to make the airplane skid around the turn.....
Good Luck