Rendering 3D vectors

Recently I have been how to use matrices with vectors. After studying books a few times, i think i’ve got the majority of information I need for now. There is one problem I have which I keep thinking about though.,

How do you render a 3D vector within a 2D environment? I’m not sure if this is a silly question or I’m just overlooking something but I can’t seem to find an answers to my problem.

You should check out http://www.glprogramming.com/