It is the staple exercise for building muscle mass and strength in the chest. The primary muscles that are worked in a bench press are the triceps brachii and pectoralis major with the anterior (front) deltoids, traps & back as secondary muscles used in the flat barbell bench press.
The person performing the exercise lies on their back on a bench with a barbell grasped in both hands. They lower the barbell to chest level, then press the barbell upwards, extending the arms until the elbows are locked out. This is one repetition (rep).