How does volcano form and erupt?

Formed-

Volcanoes are formed when magma from within the Earth's upper mantle works its way to the surface. At the surface, it erupts to form lava flows and ash deposits. Over time as the volcano continues to erupt, it will get bigger and bigger.

Erupts-

When it's underneath the surface, the molten rock is called magma. When it reaches the surface, it erupts as lava, ash and volcanic rocks. With each eruption, rocks, lava and ash build up around the volcanic vent where the material blasts out of.