Continental outlines fit together like a jigsaw puzzle. The Earth's crust is thin and fragile. The Earth's interior is still warm and active. Motions in the Earth's interior crumple and break apart the thin crust and permit fresh molten material to reach the surface. These plates grind against one another, split, and collide producing many of the geological features we see on the Earth's surface today.
Old crust is destroyed where plates collide as it subducts back into the Earth's interior.
Mountain ranges are built where plates collide. It takes only 100 million years for erosion to erase a mountain range. If mountains were not continually built by plate collisions there would be no mountains on the Earth. Earthquakes occur where plates move relative to one another. In southern California two plates are grinding past one another.