Why does an erect penis point upwards?
When you become a husband and it is time to have sex with your wife, your erect penis will be placed in your wife's vagina. The opening for a woman's vagina is in the same place where your penis is at. The vagina does not run straight in; it angles upwards toward the uterus, which is roughly behind the belly button. The angle allows the woman's vagina to adapt to the length of her husband's penis.
The angle of your erection is caused by a ligament in your pelvis that attaches to the top of the penis near the back. Because the length of the ligament varies and because it can be stretched, the direction of an individual man's erection varies. It doesn't make much difference as there is enough play in an erect penis to go the direction it needs to go during sex.