First things first, you need an appropriate bench to start this off:
You should take care that it has sure footing before you start off as any mishaps during presses, especially decline, can be dangerous. Also, it would be good to have your own spotter, especially if you’re just starting out.
The mechanics are quite similar to the bench press, in that you move weight from your chest to full extension of your arms. What differs here is the angle at which your arms are in relation to your chest.
You need to make sure that the bar is at your chest level before you lift it. Bring it down to your sternum and then push explosively till you lock your arms out. Repeat for 8 – 10 reps.