For your first training hill flights you will remain in an upright position and probably will not have time to sit into your harness. Your feet and knees will remain together during flight and the initial landing stages. Your hands are now part of the aircraft and must remain on the controls (brakes/toggles). Everything you do with your hands will cause the glider to react. Everything you do to the glider via the controls or weight shift, the glider will respond to. Smooth and subtle movements will cause the glider to react smoothly and subtly. Large, sharp and jerky movements will cause the glider to react quickly and sharply. This means that you must not reach your arms out for balance, adjust the harness, or grab harness straps to get comfortable.
Once airborne the controls are very easy. Pulling gently on the right control will cause the glider to turn right. Pulling left will cause a left turn. You should have your elbows bent with your shoulders, elbows and wrists relaxed. Your hands should hang at about shoulder level with 3-5 pounds of pressure on the brake lines. You may need to do several shallow and gentle turns to set up for a landing. Your instructor will talk you through the process on the radio.
Do not under any circumstances pull the brakes all the way down while you are at an elevation higher than 3 feet above the ground. Doing so may stall the glider and stop it from flying. Throughout the flight you will maintain your horizon reference and maintain your intended flight path.