Set the appropriate weight matching your fitness level and training type. Sit on the bench and grab the machine handle grips.
From the starting position move both machine arms in parallel by pressing and stretching your arms forward and elbow extension. Return from that position to the starting position in the same way. Inhale while beginning the motion in the starting position and exhale while pressing your arms forward.
Prepare the appropriate weight taking account of your abilities, overall fitness level and training type. Start with lighter weight to master the technique well. Return to the starting position with slow, controlled motion rather than quickly relaxing your muscle tension. Make sure your torso is fixed while pushing to avoid lower back bending.
It is better to exercise with assistance of a partner or trainer when using heavier weights.
Machine bench press is a worthy alternative to barbell bench press that should be considered by trainees with history of injury (especially of the shoulder joint but also of elbow and other involved joints and muscles), senior athletes and those prone to joint problems.
Of course, there are more advantages: you need no spotter and the weights do not put strain on your joints at the end of the reverse movement.
The trajectory is usually shorter than in bench press and as a result the shoulders are not under such a stress.
Machine bench press is not such a muscle-packer as barbell bench press because the movement is more isolated and limited. It is, however, a perfect solution for many athletes who cannot work with barbell for health and safety reasons.