Which layer of the Earth makes up the tectonic plates?

The Crust is split into what is known as 'plates' this is why they are also known as 'tectonic plates'.

Where plates meet is called a plate boundary, the plates are split into two groups, heavier continental plates & lighter oceanic plates.

They 'move' on convection currents made from nuclear reactions from inside the Earth's core.

When transform boundaries (San Andreas Fault for example) is when two plates move against one another in a horizontal direction, they do not smoothly pass one another, a build up of energy occurs along this plate boundary & once the stress build up goes over threshold, a release of energy causes an Earthquake to happen.

Divergent boundaries is when two plates move apart (an example is the North Atlantic Ridge), earthquakes rarely if not do not occur on these boundaries, when this happens on land, valleys often occur & once they get too large, they end up opening up to the ocean & become a sea basin, if they open up under water, due to how far they are from the mantle, molten rock usually fills up the gap.

Convergent boundaries is when two plates are colliding (a great example is the Himalayas), usually when oceanic plates collide, they begin to 'ride up' upon each other & can create land mass in the middle of the ocean, when this happens on continental & oceanic plates, the heavier continental plate pushes the lighter oceanic plate down beneath it & the pushed down oceanic plate melts away in the mantle, when continental plates collide they 'ride up' upon each other & create mountain ranges which usually grow very quickly & high.

Hope this helps.