To put it shortly, water causes erosion of land mass as it passes rapidly over. Think about how the Grand Canyon was formed. Wind on the other hand causes gradual erosion through the force of itself or its force along side of a catalyst such as sand which eventually degrade rock and stone or cause dunes. Tectonic motion is the force which is constantly changing the face of the Earth's lithosphere. So what happens is the continents on earth grow. The growth and decline of land mass is caused my the tectonics plate's movement on the gooey asthenosphere. they push each other. Over a period of time this force create the mountains and valleys you see today
hope this helps
