When two tectonic plates meet or collide, it is called a convergent boundary. The force behind two plates colliding can cause mountain ranges to form, as well as the formation of deep sea floor trenches.
When two plates collide, the front edges of the plates fold and bend. The folding and bending causes rocks to break and slip, which causes earthquakes.
Other types of boundaries that occur with tectonic plates are divergent boundaries and transform plate boundaries. A divergent boundary takes place when two plates move away from one another; a rift forms, and lava leaks out. A transform plate boundary is defined as two plates moving past each other with no contact.