Physiologically speaking the bench press is a mass builder. The average person needs to lift betwen 4 and 8 reps to add lean muscle mass. This varies by person though. An in shape person should be able to go to 20+ pushups before failure. This rep count begins to train the muscle fibers for endurance, but not power. If you want to get bigger, eat a lot and do lower reps. This is general advice, some people grow with reps of 10 - 12, play with it. When your muslces feel like they're swelling up, you're doing it right.