Note this machine can be used as a reverse pec deck to focus on your delts (back) muscles. The pec deck machine focuses mainly on your chest pec muscles (pectoralis major) and supporting muscles..
First things first, adjust the seat so that when you are sat down, the handle bars line up with the middle of your chest (nipple line). Make sure your shoulders are back and down. Once ready, grab the handles, with a tall chest and slight arch in the lower back - drive the handles forwards and together ideally flexing your triceps at the top for a peak contraction. Return in a controlled manner back to the starting position where you should feel a deep stretch.