Plate tectonics looks at Earth’s outer layer. It is made up of large, moving pieces called plates. All of Earth’s land and water sit on these plates. The plates are made of solid rock. Under the plates is a weaker layer of partially melted rock. The plates are constantly moving over this weaker layer.
Think of the Earth as an egg. The outer hard shell is the lithosphere or "hard rock" and the next layer or egg white is the mantle. The central core has two parts: the outer is more liquid and the centre is more solid. Much like a convection oven, the heat from our core shifts these pieces to form the Earth we know and love today.