What moves the plates?

The core of the earth under the lava is so hot, that it makes the magma under the crust move, which causes it to move in a pattern called a convection cell, which basically is a pattern where the magma rises, cools, and goes back into the mantle. The path that it is moving in is called a convection current, and depending on which way it rotates, (anti-clockwise or clockwise), the plates will move in that direction. The crust then spreads in two different directions: apart from each other, and directs outwards. The old segments of the crust will then end up under the earth, heated up by magma,  and the new rock will be formed at the top.