They move thanks to convection currents. Convection currents all start with density. Density is how much “stuff” (atoms and molecules) that are packed into one thing. If something has a high density, all of the atoms and molecules are close together and will sink. If something has a low density, the atoms and molecules are spread out, making it float. Convection currents work using the change of density. When things get hot at the bottom of a container or the Earth, it starts to get less dense. That means that it starts to float up. As it makes it’s way to the top, where there is not much heat, it starts to cool down and sink back down again. This process happens over and over again creating a circular current that actually moves continents on Earth!