The Continental Drift theory explains the creation of the seven continents that we currently have. just to give a background, tectonic plates are giant pieces of land (the crust), floating on top of molten silicate material. (the mantle). The crust is composed of a lot plates. Now, all of these plates move, which result in what we call earthquakes.
Now back to the main topic, hundreds of millions of years ago, the Earth had one giant land mass, a super continent named Pangaea (which literally means "All of the Earth" in Greek). Now, because of plate movement, (to cut the story short) Pangaea split into two major land masses. These land masses split until the seven continents were created.
Until now, the plates are still moving, and millions of years from now, the continents that we know will "evolve" since the plates will always keep on moving, creating new forms of land.