Answer:
Basically, the Earth's rocky crust (both oceanic and continental) is comprised of a series of plates that float on the semi-solid or magma-like mantle. Convection currents cause the magma to rise and fall, therefore, moving the Earth's plates in different directions. This movement is responsible for mountain building, volcanoes, and earthquakes.
Convergent Plates: When two continental plates converge or collide, the crust is squished together, folding and buckling and forming mountains. This is just one way mountains are formed.