how long must I masturbate till sperm comes out

Your question is very strange. When  you start masturbating  the penis will slowly become  erect and  big. After stroking for a few minutes you will experience a pleasurable sensation and the semen from the penis will be released at jet speed. At that time you will get a pleasurable sensation. This can be done by solo. If you have a close and trusted friend you may do mutual masturbation.

Generally some other person especially the opposite sex  touches and fondle the Penis it will be more interesting and pleasing act.