Glad you asked...
You can do an experiment to make your own penicillin, but don't actually use it to try to cure anyone. Real medicinal penicillin needs to come from a doctor and a pharmacy. Penicillin comes from mold that is grown on bread or citrus. Here is the experiment that shows how to make penicillin: http://www.howtodothings.com/health-fitn...
Then again, this answer might help you...
If you've ever had mold develop on a loaf of bread after it's had some moisture for a while, you've basically made penicillin. Penicillin is a grown in laboratories with advanced equipment because extracting the right type needed for medicine is difficult.

