Convection is a term used to describe the movement that results from the heat at the core of the Earth moving through the layers of the lower and upper mantle to the surface of the planet. As any given layer heats, it expands, which causes slight movement on the surface of that layer.
Tectonic plates are masses of the Earth's lithosphere, the outermost layer of the mantle. As the rock underlying the tectonic plates moves in response to the heat being transmitted by convection from the Earth's core, the tectonic plates are also moved.
Dissipation of heat from the mantle is acknowledged to be the original source of energy driving plate tectonics, through convection or large scale upwelling and doming.
Areas in which the lower layers of the mantle are broken and subjected to greater heat intensity (observed by the presence of volcanoes, hot springs, or cracks in or between plates) move more rapidly because the convection of more heat is causing the asthenosphere to expand more quickly.