Just trying to make rooms

I've been trying to find a truly deep and comprehensive tutorial on mapping, but can't find one that's extensive. I just want to slice into a face and make an opening for a room. I've been able to subdivide a face but it's only dividing it into a grid. And with edge tools I can't make straight lines, I've tried holding Ctrl and Shift and Space etc., but it's all freeform.

I'm basically looking for a hole-punch type tool

you are describing the carve tool from source 1. It created terrible geometry. You have to use the vertex, edge, and face selections, and extrude, slice, and scale.

If you want to learn to use the map editor it is very similar to modeling.

Look up a modeling 101 video and I bet you will find what you are looking to do on it.

turn on grid snap and also press shift + X for the cutting tool. use [ and ] to change the grid size quickly