Learn
PhET
Build a virtual circuit and see why the bulb lights
BrowserFree web simulations · not real wiring instructions
Open PhET Why this one
Change one part of a simulated circuit and watch the result. Useful when you want to experiment with a science concept instead of only reading an answer.
Try this first
Open Circuit Construction Kit: DC and connect a battery, wires and a bulb into a loop. Change one value and compare the current or brightness before changing anything else.