There are three types of plate boundaries: convergent, when tectonic plates come together; divergent, when tectonic plates are moving away from each other; and transform, when two plates are sliding past one another. Each boundary serves a different purpose, and mountains are also the result of activity on these boundaries.
Divergent plate boundaries form long fissures in the Earth's crust. These fissures allow for magma to seep from the Earth's mantle and create geysers. Convergent boundaries are responsible for the formation of mountain ranges or oceanic trenches, depending on how the plates involved behave. Transform plate boundaries are unique in the fact that they do not create or destroy tectonic plates. Transform boundaries are notorious for causing earthquakes in the area surrounding them.