The extrude tool is one of the most basic polygon tools available. It is very useful if you want to increase the detail of a polygon mesh. See the pictures below to understand want the extrude tool does.

A similar effect can be obtained with the combination of the cover tool and the transform tool. The cover tool even allows to extrude edges and is in many situations more comfortable than the extrude tool.

Modes
The extrude tool can only be applied to raw polygon objects. It's only available in polygon mode.

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  To use the extrude tool, select some polygons of a raw polygon object. Then choose the extrude tool and drag the mouse in the 3D view either to the left or right, depending on whether you want to perform a negative or a positive extrude. Once you are finished release the mouse button.

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Properties

• Preserve group: If this property is checked, the extrude tool tries to preserve the grouping of the polygon selection. It therefore calculates the angle between the neighboring polygons which are also selected. If the angle between the polygons is smaller than the angle property of the extrude tool, the group of these polygons will be preserved.
• Angle: See preserve group.
• Quantize: Set this property to 0 if you want to extrude continuously, otherwise this value determines the distance you want to quantize the extrude to.