The decline bench press works your pectorals and triceps.
To do this exercise you should have a decline bench and then on the straight bar hold the right hand right above the right shoulder and the left hand right above the left shoulder and grip the bar. Make sure you get the technique right before you add any weights. Sometimes the bar will have rings so just position your hands on either side of the ring. Bring the bar down towards you chest and push back up make sure that you keep this nice and slow so you can get maximum benefit. You can also use dumbbells for this exercise.
1st set do 10-15 reps on say 20kg (if you’re starting)
2nd set do 8-10 reps on 25kg-30kg
3rd set maintain 25kg-30kg and do 8-10 reps
4th set go back down to 20kg and max out.
Try and move up every week, if 10kg is too much to move up by every week then move up by 5kg. Do it on how comfortable you feel.
[image from workoutlabs.com]