HaloMods "Classic" Read-only Archive

I have a question about making new faces. Now, I usually use the middle mouse button and alt to move around my model. But, if when I am creating a new face, how can you still move around. Once I start selecting my vertex's if I go to move I lose the vertex's I already selected. I saw a video tut where the guy was doing just this. Can anyone help me out?

Left click outside the model and then you can move around and not loose the points you already clicked.