Tectonic plates are the name of the pieces of land forming the upper layer of the earth.
They are not fused so they can move.
When these big plates move, they generate friction at the bounds, and that is what we call earthquakes.
At the beginning of the history, these plates ride on each other, and the one that goes upper creates the mountain cordons we know today.
Another natural hazard is when the pressure of the core magma goes up through those borders, and create volcanos.