There is no manual that comes with the penis. For most men, the genital is something that you usually get to learn about in a trail and error process throughout life.
If all was right with the world, we should all get instruction manuals with our body, both males, and females (especially females). These manuals should come with full diagrams, figures and maybe an entire chapter on how to use the penis to successfully give orgasms to your partners.
Truth is there are proper and improper uses of a penis, and here are the improper uses:
1. DON'T bend a hard penis.
By all standards, the male penis WAS never designed to bend at extreme angles. This is most especially essential when your "third leg" is in a fully erect state. Never try to bend the penis over 30 degrees.
2. DON'T steam clean the balls.
As tempting as it may be, wrinkled testicles are normal and any attempt to steam clean the penis will result in grievous injury. This should also go without saying that you shouldn't try to "botox" your testicles.
3. DON'T apply excessive friction to a penis.
Some friction is encouraged during a masturbatory session (heck, even sex is all about friction), but vigorous friction could result in what is basically rug burn. From personal experience, applying too much friction to the penis will probably result in a trip to the hospital.
4. DON'T slap a penis.
Sometimes your penis can act up; like getting an erection in public or not getting an erection when it has to, but please this doesn't ever mean you should slap it. Please, don't.
5. DON'T attempt to put anything inside the penis.
The opening at the head of the penis is not designed to allow objects to pass into the penis. DON'T place anything inside the penis or obstruct the opening.
6. DON'T clean a penis with household cleaners.
You might be tempted to treat the penis as if it was the countertop in your kitchen, but abrasive household cleaners are going to be harmful to the penis's integrity. Soap and water will do just fine, no matter how dirty the penis gets.
7. DON'T bite a penis.
The skin surrounding the penis is incredibly sensitive and puncturing it could result in serious injury. SERIOUSLY!!! It's never right to bite the penis, no matter how kinky it feels
8. DON'T stand on the penis.
Penises are non-load bearing (YOU KNOW WHAT I MEAN). DON'T put your full weight on the penis, or serious injury could occur to both you and the penis.
9. DON'T test the elasticity of a penis.
DON'T pull on the penis past the point of resistance. Despite some tensile strength, the penis was not designed to be stretched.
10. DON'T apply excessive pressure to a penis.
The penis is incredibly sensitive and is not designed to withstand blunt force trauma or large amounts of pressure.
But since we don't live in utopia and this is not true, consider this post your guide on how to NOT use your penis, because I am going out on a limb here and think you're probably familiar with the proper uses of your manhood.