After you draw your walls, start with the layout tool to build out your floor plan. This view is great for when you just want to start with a simple wireframe view of your space. Place simple symbols into the space and after changing the appropriate settings, these will translate into 3D models that you can continue to develop in the 3D editing views.

If you don't want to start here, you don't have to. Move straight to the Public and Enterprise libraries and being working in the that view with 3D models but this will not produce a wireframe drawing in the Layout view if you choose to go back to it. (Basically, it doesn't link backwards to Layout)