Typically beginners start with the "yank and bank" method of turning.

If you use the ailerons to put the plane into a banking turn, the planes wing will lose some left because the wings are not level to the ground anymore. This will cause you to lose altitude. If you give a LITTLE up elevator when turning, you can maintain your altitude while turning.

When learning, never bank the plane more than 45 deg. Any more than that, and the plane starts to fall like a rock.