This exercise mainly targets upper pecs/ upper chest exercise. The secondary muscles targeted are triceps and shoulders. You need a incline bench and a set of dumbbells to do this exercise.
How to do Hammer Grip Incline Dumbbell Press
Recline on the incline bench. Let a spotter hand you the weights. Start with palms facing each other and elbows bent. Now lift the arms in explosive fashion and lower them slowly in controlled fashion. Form is and important factor in chest exercises.

Video Demo 1