Extrusion Modeling in 3D Modeling

In 3D modeling, there is a very good tool called extrusion. Extrusion allows you to either collapsing a face by making it smaller or by extruding the shape outwards along the normal surface. If you extrude a quadrilateral shape will create four new polygons to bridge a gap between the starting and ending position. Unless you know what it is you are after, it can be very hard to imagine what it will look like when you extrude the shape.

This is showing the extrusion of a model