Penis
A Penis is a multi use tool
A Penis may be used for the following..
 1. Pissing into the toilet bowl
 2. Having a wet dream
 3. Giving oral satisfaction to a woman or a gay male (either one can give you a blow job)
 4. Receiving satisfaction from a woman or a gay male (one or the other giving you a blow job)   
 5. Sexual intercourse (straight)
 6. Sexual intercourse (anal) 
 7. Showing off to the guy standing beside you at the urinal
 8. Shaking off drips after pissing in the urinal
 9. When you are a small boy you may use it for striking a bargain with a small girl. 
The conversation usually goes along these lines "You show me yours and I'll show you mine" 
10. Masturbation
11. CBT (Cock and Ball Torture) or Genitorture (BDSM specialities)
12. Another area of the body to receive a few tattoos
13. Another area suitable for body piercing
14. It's a good part of the anatomy for wearing a ring
15. A hard penis is good for the ejaculation of semen
16. It may be stimulated to give you pleasure 
17. A penis fits neatly into an orifice. It may fit into more than one orifice, usually one at a time. 