There are a number of different types of plate boundary.
A destructive plate boundary is sometimes called a convergent or tensional plate margin. This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate [continental plate: A section of the crust that makes up the Earth's landmasses.] . Friction causes melting of the oceanic plate and may trigger earthquakes. Magma rises up through cracks and erupts onto the surface.
An example of a destructive plate boundary is where the Nazca plate is forced under the South American Plate.
Collision zones form when two continental plates collide. Neither plate is forced under the other, and so both are forced up and form fold mountains.
A constructive plate boundary, sometimes called a divergent plate margin, occurs when plates move apart. Volcanoes are formed as magma wells up to fill the gap, and eventually new crust is formed.
An example of a constructive plate boundary is the mid-Atlantic Ridge.
A conservative plate boundary, sometimes called a transform plate margin, occurs where plates slide past each other in opposite directions, or in the same direction but at different speeds.
Friction is eventually overcome and the plates slip past in a sudden movement. The shockwaves created produce an earthquake [earthquake: A sudden shaking of the ground which releases energy.] .
This occurs at the San Andreas Fault in California.