The Earth is made up of different layers:
The crust is the outer layer of the Earth. It is a thin layer between 0 - 60 km thick. The crust is the solid rock layer upon which we live. It is either continental or oceanic. The earth's crust is broken into plates. Heat rising and falling inside the mantle creates convection currents generated by radioactive decay in the core. The convection currents move the plates. Where convection currents diverge near the Earth's crust, plates move apart.
Where convection currents converge, plates move towards each other. The movement of the plates, and the activity inside the Earth, is called the theory of plate tectonics.