This exercise targets lower pecs / lower chest area. To do this exercise properly get into standard push up position and keep some kind of strong furniture like a bench or chair under your fists/palm hence raising them above ground. Now do the regular pushups squeezing you pecs simulating the effect of Incline bench press. Triceps are also trained in this exercise. These are more suitable for beginners as they are easy and help in developing strength to do regular push ups or decline push ups.
Video demos on how to do decline push ups or flat bench push ups.