Okay, so imagine you have a little toy car that moves when you wind it up with your hand. The car moves because your hand has put energy into it by winding the spring. Now imagine instead of using your hand to wind the spring, we want to use something that doesn't need to rest and can keep going for a very long time.
So we use something called a nuclear fuel source, which is like a tiny little battery that gives off a lot of heat. We put this fuel source in a machine called an advanced Stirling radioisotope generator.
Inside the generator, there are two things called pistons. These are kind of like the little arms on your toy car that move it forward. Except in this case, the pistons move back and forth because of the heat from the nuclear fuel source.
When the pistons move, they help create electricity. Electricity is what powers your toys and your TV and your lights! So the advanced Stirling radioisotope generator is a machine that can make electricity without us having to use our hands, and it can keep going for a very long time because of the nuclear fuel source inside.