There are three main types of volcanoes: shield volcanoes, cinder cone volcanoes, and composite volcanoes. They are named based on their shape and composition. Volcanoes are openings in the Earth's surface where molten rock and gases erupt. They contain features like magma chambers and layers of ash and lava. Caldera volcanoes have large, cauldron-like depressions at their summits. Composite volcanoes are tall with small craters and layers of both lava and ash materials. Compound volcanoes have multiple vents. Shield volcanoes are flat and release lava slowly down their sides in non-explosive eruptions.