My penis length is around 5 inches when erect, i want to impregnate my girlfriend she also want it what should be done, please help...tell me in detail.

Congratulations: You're an average guy and won't have any of the problems that guys who are kind of small or way too big run into. If you are sure you are ready to be parents, simply start touching each other in ways that give you both pleasure. Move around the body until you get to the genital areas, and become aware of being excited and delighted by each other. One of you will know what to do.