If you wish to walk though you model, select 3D perspective view, not 3D axonometry view. At the bottom of the 3D window there is an button with a silhouette of a person. Hit that button and it will show you splash page with the commands to use to walk through the model, close that and you should be able to use classic WADS (if you're a gamer, you will understand) to navigate or "fly" in your model like you're in a first person perspective video game.
