Initially the bell of the plunger will be full of air. Make sure the first thrust is gentle as a hard push will force the air back around the seal and splash water all over the bathroom.
After the air is out of the plunger, plunge forcefully in and out while maintaining the seal. This forces water in both directions of the drain which will loosen most clogs. Plunge about 15-20 times to start.
If the water level drops Eventually the clog will loosen and everything in the toilet will go down the drain. Take your gloves off and give yourself a pat on the back.