Typically volcanoes are classified into various types based on their shape, the composition of the magma and the way that they erupt. Geologists group them into the following four major types of volcanoes:
• Composite volcanoes are the result of multiple eruptions occurring over a prolonged time period. These formations are made by alternating layers of lava and rock fragments. They have steep sides and can usually exceed heights of 2500 m. Most such structures have a crater at the summit with a central vent. This central vent can be accompanied by other clusters of vents.
These types of volcanoes can be so quiet in between eruptions that they seem almost extinct. When a composite volcano becomes dormant, erosion begins to destroy the cone. After many years, the great cone is stripped away and eventually all traces of the cone are worn down. However, they can cause quite a stir upon eruption as they detonate in an explosive way. Usually large and conical in shape these volcanoes are constructed along the edge of tectonic plates. Mount St Helens, Mount Fuji and Mount Kilimanjaro are well known composite volcanoes.
• Shield volcanoes are huge formations with broad summits and low slopes. They are built by many layers of runny lava flows. Lava usually spills out of a central vent or group of vents. The resulting shape is a broad, gently sloping cone structure. Since the lava is very fluid, it does not pile up into steep mounds. Instead, it travels down the slope for long distances. These volcano types may build up gradually over time creating multiple layers. These structures may be produced by hotspots where the eruptions are of low explosivity. The Hawaiian Islands especially Mauna Loa and Mauna Kea are well known shield volcanoes.
• Cinder cones are steep conical hills formed from particles and blobs of hardened lava above a vent. These lava blobs usually solidify in mid air before they land on the ground around the vent. Over passing time, these types of volcanoes build up into rounded or oval shaped structures. Most cinder cones have a bowl shaped crater at the peak and rarely exceed 250 m in height and 500m in diameter.
Although the most common volcanic formations in the world, cinder cones are the least complex type of volcano. Cinder cones can occur alone but usually grow in groups. Cinder cones can grow rapidly and modify their shape when the position of the vent changes.
• Lava domes are rounded formations made by small masses of lava that are too thick to flow very far. The viscous lava from these domes just oozes out and spills over and around the vent. The dome grows by accumulation of the 
hardening lava, and the structure grows from material spilling off the sides of the dome. These mounds can grow for many months, even years with the sides being very steep. Lava domes are threatening as these volcano types can explode violently without prior warning releasing a huge amount of rock and ash. Mount Pelee in Martinique is such an example.
So while, most people relate the well known cone shaped structure to being a volcano, they can also be found in other shapes. The various types of volcanoes can be found in the Ring of Fire which nestles over 50% of the world’s volcanic structures.
More information about different types of volcanoes here:
Types of volcanoes in Yahoo Answers
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