The function of the organ penis in male reproductive system is - 

The male reproductive system consists of :

Testicles (testes): A pair of oval-shaped organs masked in a pouch called the scrotum. They are responsible for the production of sperms and the male hormone testosterone.
Scrotum: It is a sac-like organ that hangs below the penis and behind it. It is the houses of the testicles, or testes, and maintains a temperature that is required for the production of sperm by it.
Vas deferens: The sperms produced in testes are stored in a tube called the epididymis. Here the sperms get matured and pass to urethra through the muscular tube called vas deferens.
Accessory glands: This includes three glands, namely seminal vesicles, prostate gland, and Cowper’s gland. The secretions from the three glands mix to form a fluid called semen. Semen nourishes the sperm, increases the volume and helps in lubrication.
Penis: Penis is a cylindrical tube which serves as both reproductive organ and an excretory organ. It delivers sperms into the vagina during sexual intercourse.