How does the theory of plate tectonics relate to volcanoes?
Suggest you do a search in Socratic for "volcanos" and "plate tectonics" on this subject, but here is a bit more to help you out.
Volcanoes are an indication that the Earth's mantle (below the crust) is in motion and things are going on below the surface. Volcanos form in 3 basic locations: 1) along divergent spreading centres where the crust is being pulled apart, 2) along convergent boundaries where a slab of rock is being subjected back into the mantel and it is being partially melted bringing up new magma, and 3) along hotspot locations, such as Hawaii.
Volcanos in the Philippines are associated with a convergent margin in which oceanic crust is being subducted below other oceanic crust. As one slab goes down, it undergoes partial melting and magma starts to rise up again, break the surface and result in volcanic eruptions from time to time. Often called " back arcs". See pic.