Skips and skids are done differently.

Skid stopping for beginners: cinch up your toe straps tight, lean forward to the stem, stiffen up your back leg and push down while pulling up with the front leg. In time, you'll develop the muscle and technique and be able to do these sitting down.

Skip stops: get off your bike. Have one foot in front of the other and try to jump 6 inches forward without bending your knees. This is the same motion you use to unweight the rear wheel / "skip" while the pedals are at 3 and 9 o clock. Learn it with both feet forward, than learn it with your feet at different positions than 3 and 9 o clock.