Most gyms offer barbell bench press stations in their free-weight areas, but if you don't see a standalone station, most squat racks can be used as bench presses if you pull a flat bench to the station and set it up under and perpendicular to the bar. If you're new to performing the bench press, ask a friend or trainer to spot you before you go it alone.
Lie back on the bench with your torso flat, your knees bent, your feet on the ground. The bar should be positioned just over your shoulders so when you lift it off its rack, you must bring it forward slightly to situate it over your chest. Engage your core and press the bar up off the rack. Extend your arms directly over your chest, your wrists straight, your palms facing away from you. Inhale as you steadily lower the bar toward your chest, bringing it within about an inch or two of your sternum. Allow your elbows to come down at an angle, pointing them away from your torso at about 45 degrees. Exhale and press the bar straight up, extending your arms.