Volcanoes are formed when one plate goes underneath another. This process is called subduction. When subduction occurs, magma pushes upward, and exposes out on the crust. Then a volcano erupts. Dormant volcanoes are volcanoes that didn't erupt for a long time but are still active. Active volcanoes erupt multiple time in the past years and extinct volcanoes can't erupt anymore.
Subduction Mount Fuji, Japan Mount Vesuvius, Italy
Subduction Mount Fuji, Japan Mount Vesuvius, Italy