How do you make your penis become hard?

To make your penis become hard and erect you need either physical or mental stimulation.
If you're a teenage boy, it doesn't take much.
put pressure on it especially under the head.
Squeeze it
Rub it fast and play with it.
You can jack it off to make it hard.
You can touch it until it gets hard.
You can get a handjob or blowjob.