To change window viewpoints, highlight that window, and select either Top View, Side View, or Front View from the View menu. In order to add or subtract primitives into our world, we need to be in Modify Mode. If you have never worked with a 3D editor before, a primitive is a primitive shape that is used to build the objects in our world. In this example we will be using a single primitive to create a square room. We use these primitive shapes to form brushes.
Brushes form all the walls, and shapes on our levels.
For example if you were to create a level of your house, the walls, ceiling, and floor of each room would be a distinct brush. We would create a brush for each room, and by connecting these brushes, we would form your house. Additional objects such as a table, would also be formed by brushes, which would be added into our rooms. I want to give a brief description of a couple of the options however, for future reference. The size options and wall thickness should be pretty self-explanatory.