Extrude selected vertices and edges to make a 3D shape.
After executing the Extrude action, the tool reverts to the Move Tool. Drag the newly duplicated and selected vertices to the desired length of the extrusion.
Note that you can also put a thickness on some models by extruding and then scaling to the desired thickness.
To extrude selected vertices along a defined path, use the Actions > Extrude Special > Along action.