This exercise mainly targets pecs / chest / mid section of chest. This is similar to pec deck butterflies. Lie flat on a free standing flat bench, flat on your back. Now let the spotter hand you the dumbbells keep your arms wide open with elbows slightly bent like a ‘V’ shape. Palms must be facing each other with dumbbells. Lift the dumbbells in explosive fashion as if they are going to touch each other. Squeeze your chest muscles at the peak of the motion. Lower your arms slowly to your initial position and count one.
Video Demo on how to do Flat bench Dumbbell Flyes Properly
Video Demo 2

Video Demo 3