The Extrude Tool

The Extrude Tool allows you to add more geometry on the surface of a polygon object by extruding faces or edges,
It can be found in the Polygon Tools Menu (which is on the left controller on the right side of the touchpad (HTC Vive or Oculus Rift) when in Polygon mode.
The tool is indicated by Maya’s Extrude Tool icon.

See this video for a demonstration on how to use the tool: