To do a bench press you need to lie your back flat on a bench, grip a barbell or 2 dumbels with hands wider than shoulder width, directly over your shoulders. Press your feet firmly into the ground and keep your hips on the bench the whole time. Next, keep your core engaged, and slowly lift the bar or dumbbells off the rack. Lower the bar to your chest with your elbows at a 45* angle, and press feet into ground as you raise the bar. Source 1