Extrude

Extrude is a unique builder tool as it doesn't use a selection. Extrude simply extrudes and shrinks a face of the same block.

To extrude a face, use right-click. To shrink a face, use left-click.

If you're not happy with the result, use Ctrl + Z to undo the placement. If you can't make up your mind, you can use Ctrl + Y to redo your undo.

Below is a video showcasing the extrude tool.