The launch of the glider should be as close to the glider's trim speed and altitude as possible to avoid pitching the nose up (too fast) into a stall or entering too steep a dive (too slow). The glider should keep flying straight out of your hand. Once the glider is in stable flight, bring the controllable slope (here a 50cmX70cm piece of cardboard) so as to position the glider in the rising wind at the top edge of the controllable slope. Here's a video of an indoor flight (same as from first page):