See to that you secure your legs at the end of the decline bench and get yourself down on the bench.
Using a little wider than shoulder width, lift the bar from the rack and hold it straight over you. The arms should be perpendicular to the floor. This will be your starting position.
Lower the bar in a controlled fashion until you feel the bar on your lower chest.
Bring the bar back up to the starting position.
If you are executing this exercise for the first time, see to that you have an experienced spotter.
See to that the bar touches your lower chest.