These two theories are related because they are continuity from one another. The theory of plate tectonics insinuates that the crust layer is broken into multiple pieces, this is caused by the pressure of the mantle layer, which managed to break the crust where it is thinner. The theory of continental drift insinuates that the tectonic plates move around the Earth because of the pressure from the hot semi-liquid mantle layer.
The difference between continental drift and plate tectonics is that the theory of continental drift states that the world was made up of a single continent.The theory of plate-tectonics, on the other hand, states that earth's surface is broken into numbers of shifting plates or slabs.
