How can you be a donor?

It depends on two factors.those factors are why do you want to be and sperm donor? are you doing it for money or are you doing it for the good of helping infertile couples? if you want to donate to a sperm bank you would have to undergo certain test and provide sperm samples when needed.in other Words you would have to make a commentment to the sperm bank.if you just want to donate for free,my advice would be for you to go to your doctor and get tested for STD's and HIV.also a sperm test would need to be done to inform the recipents that you have an acceptable sperm count.