Do you remember those one-way streets you saw while riding in the car? You could only go one way on that road, but the other way was blocked off. Diodes work just like those one-way streets, but for electricity!
Diodes are little electronic components that only allow electricity to flow in one direction. They have a positive end and a negative end, and when you connect them to a circuit, the electricity can only flow from the positive end to the negative end. If you try to connect it the other way around, the diode will block the flow of electricity, just like a one-way street.
Diodes are used in lots of electronic devices, like radios and computers. They help make sure that electricity goes where it's supposed to go, and that things don't get broken. Pretty cool, huh?