GPS Position Hold enhances the auto-level mode to also keep the copter in the same position. It will bank the copter in order to counteract any external force such as wind. Now when you enable this feature the copter stays in one spot!

GPS Return to Home (RTH) when enabled will take full control of the copter, turning it toward the home position and then flying on it's own back to the set home position. The home position is set each time the copter motors are armed. Lost orientation of the copter? Lost sight of it? Turn on the GPS RTH and it will come right back to you. Hopefully, there are no trees or low flying planes in the way! It isnt that smart.