/3/ - 3DCG

I have some experience in 3d modeling, along with some CAM programs(subtractive manufacturing), But when I try CAD(additive manufacturing) I'm completely fucking lost, lads. Booted up fusion 360 last night, managed to make a basic hollow box with no top. But the workflow from 3d modeling, to CAM, and then to CAD is so entirely different. Couldn't figure out how to make a god damn square hole in the bottom of the box.

Any fusion 360 nerds here? In a 3d modeling program i'd use a simple boolean operation, in a CAM program like featureCAM I'd put layout lines ontop in the center of the part, and offset additional lines from there to form my hole. What would it be called for something like this in CAD?

I tried using the hollow tool on the inside face of the box, but it just throws an error and won't let me do it.