I have a simple model of a building. I use the extrude tool to push an external wall surface in by 1 foot. With the extrude tool still active, I use the mouse to move to another surface and double click that new surface. Instead of pushing the surface in 1’ it pulls it out 1’.
I am watching a tutorial, and it does the opposite in the tutorial. I am on a mac, and the tutorial is being demonstrated on a PC.