How are hot spots related to plate tectonics?
A moving tectonic plate over a hot spot will lead to over time a long chain of volcanoes.
The best example for a hot spot is the hot spot in the pacific ocean, that hot spot that produces the long chain of volcanoes known as the Hawaiin islands. A hot spot as you may or may not already know is an area where lava rises from the earth to the surface. The lava cools down and forms a volcano. The hot spot itself never changes position, but the tectonic plates are constantly moving, so the volcano formed will "move" along with the tectonic plate to the direction where ever the tectonic plate is heading, but at the same time the hot spot doesn't stop producing lava.
When the tectonic plate moves, another volcano is formed, and over time as the tectonic plate moves, that volcano moves towards the direction that tectonic plate is moving, and the process repeats. That's exactly what has been happening to the Hawaiin islands, and over time those formed volcanoes might descend deeper into the ocean until they are no longer islands.