When Sl is depressed, Cl begins to charge to the supply voltage. That places a forward bias on the gate of Ql turning it on and supplying current to load resistor RL. When the charge on Clleaks off, the transistor shuts off, cutting off current to the load. That load could be anything from a transistor radio to a child`s toy.
Transistor Ql, is rated at 0.5 A at 60 V de. With a supply voltage of 9 V de and with Cl rated at 0.22 J