An orogeny (or orogenic belt) is created when a continental plate is being squeezed; this forces the Earth’s lithosphere (crust and uppermost mantle) to crumple and pushes part of the continental plate upwards. The result is one or multiple mountain ranges. Usually this happens when two or more continental plates collide. Some examples are mountain ranges like the Himalayas, the Alps and the Appalachians.
Here is a simple example of how a mountainchain can be created.