Touching is a built-in function in Bitsbox. The code you put inside the touching function only runs while someone is touching their finger (or cursor) to the screen.
The touching function is called by Bitsbox twenty times a second, but only when you're touching the screen. It's kind of like the loop function, with a "touch" of interaction.
This program spins a stamp, but only when you press and hold on the screen.