Lie on a flat bench with a dumbbell in each hand. Push the weights together forcefully while you perform a bench press. Hex head dumbbells make this much safer and easier.
 
Purpose
The hex press strengthens the shoulders, chest and triceps like any bench press, but the push of the dumbbells together creates more and different tension in the pecs to help encourage more growth.
 
Programming
Generally sets of 6-15 reps are appropriate.