The Andes was formed by the oceanic-continental convergence between the western-moving South American plate and subduction of the Nazca oceanic plate
Himalaya mountains roughly 50-70 million years ago when the northward-moving Indo-Australian tectonic plate began colliding with the relatively stationary Eurasian Plate. The boundary of the collision is called the Tibetan Plateau.
Appalachian Mountains formed by plate tectonics and earthquakes shifting weight into each other causing large mountain ranges to form.