The Bench Press is an upper body movement which works through your pectoralis major, anterior deltoid, triceps and biceps.
To set up your feet should be flat on the floor and you back lying flat along a bench. You should have postponed the bench underneath the rack and the bar such that you will be able to lift the bar off the rack while in this position.
Grab the bar with your hands equal distances from the middle and your elbows vertically below your fists. Press the bar up into the air so that it is vertically above your shoulders. From here bend your arms down so that your elbows are at a 45 degree angle from your body. Repeat this movement working through your repetitions.
To add power to this movement you can exhale as you push the bar up and into the air.