Put the band around your thumbs then around your back. Keep your elbows in or the band will roll up your neck. Hands shoulder width apart. Body straight like your doing a push-up. Bend your elbows and turn them in until your forehead is almost on the bar. Keep your elbows in and punch/ squeeze your hands to raise yourself back up. When you are in the bottom you want to feel a lot of pressure in the elbows right at the end of the medial tricep head.
These can be done as a main tricep movement if you set the bar low enough or have enough bands on so that 8 reps are hard or you can set the bar higher and crank out a bunch of reps at the end of your session. A good starting point for weaker athletes who haven’t Donne this before is the bar at the same height as they bench at.