It is based on creating everything out of triangles, which makes texturing and rendering easier and also prevents you creating non-convex polygons which would mess up my collision detection in the game.
It is, however, smart enough to realise when you click a counter-clockwise triangle and reverse the order appropriately.
Rather than have a messy and complex GUI, it has a system whereby when you press Tab, a text entry line appears at the bottom of the screen and you type in commands, like "grid 64" or "wireframe off" and so on.
Later, it will be possible to map keys to commands. Probably.