Weight is produced by gravity which is equal to the weight of pilot and aircraft. When lift and thrust exceeds weight and drag, the craft will climb. When weight and drag exceeds lift and thrust, the craft will descend. Thrust is produced by the propeller driven by the engine. Drag is produced by air resistance as the craft moves through the air.
Resistance is produced by the chute, the lines, the craft and pilot.
The throttle controls your climbs and descents in a powered chute rather than your speed. It does this by changing the angle of attack of the wing or that is, the angle at which the wing meets the air. When the throttle is moved to increase power, the thrust of the prop moves the craft forward. This changes the angle of attack of the wing, resulting in a climb. Maintaining increased thrust will maintain the climb.