I'm talking, as basic as it gets. If you have any idea about JK Editing, you might want to stop here, but who knows, you might learn something. So, if you want a big square room, you just create one sector, drop the player down into it, and that's it. The thing to remember though, is that when you insert a sector, you insert OPEN space, so the player can walk into it.
Vertices are points in space, represented by little dots in level editors.
Picture your cube again, and picture a dot at each corner. A cube sector is made up of a bunch of little dots. A surface is a set of at least 3 vertices, on a plane. We're not talking flying here, we're talking FLAT plane. One side of a sheet of paper is one surface.