The penis usually requires little introduction.  It has, deserved or not, been the star of sexual conversations and activities from ancient civilizations through modern times.  The penis is the primary body part through which its owners experience sexual stimulation and orgasm.   Inside the penis the urethra conveys both urine and semen out of the body exiting through the tip.  On top and surrounding the urethra are erectile tissues that engorge with blood during sexual arousal resulting in an erection.  Erections allow the penis to have intercourse and the firm tissue and taut skin allow for more intense sensations.  

The penis and its erectile tissue extend into the body towards the bottom the pelvic floor.  However, much of the penis is visible outside the body while the tip, or glans, is the most sensitive part.  Most penis owners find that some degree of moving touch, like rubbing or stroking, of the glans is very pleasurable and leads to climax.  Despite that, all of the penis can enjoy touch and texture while that does not necessarily lead directly to orgasm. 

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The exact size, shape, and color of the penis can vary greatly from person to person.   While there are average sizes for flaccid (soft) and erect penises, size has no bearing on sexual function, libido, or "quality" of sexual interaction.   It is also common to have a slight curvature when erect.  Also, depending on social and cultural factors, a penis may be circumcised (aka, "cut") and have no foreskin.  When the penis is fully erect the foreskin retracts to expose all, or most of, the glans.  There is some degree of debate and controversy over the pros and cons of circumcision, but at current it remains a personal, familial, or cultural preference.  

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Erections are often critical for most owners to experience sexual stimulation that leads to orgasm.  Greatly simplified, an erection occurs when signals from the brain travel down the spine, nitric oxide is released, smooth muscles relax, and blood flows into the erectile tissue.  However, an erection is not required for a penis to receive pleasure, though it may take some more creative experimentation with different stimulation.  

The penis shares a similar construction to the clitoris as they both possess erectile tissue, a sensitive glans (tip), and loads of nerves that respond to a variety of physical stimuli.  Besides physical size, one difference is that the clitoris is considered to have potentially twice the nerve endings.  ​​​