F5 will show the what you currently have selected in any window, whether it be plan, section, interior elevation, etc, or what you have marqueed in the floor plan. If you have something selected
and
a marqueed area, the selection always takes preference.
Either before or while you are in the 3D window, you can hit Ctrl/Cmd+F5 to view everything in 3D. Furthermore you can select elements whilst in the 3D window and toggle F5 and Ctrl/Cmd+F5 to view specific elements or the entire model. In fact you can just use F5 if you select and deselect the elements you want to see.
F3 will recall all the settings of the last 3D window you accessed, including the Filtered Elements, Axonometry/Perspective, etc as well as the previously selected elements, regardless of what you currently have selected. If the previously viewed element has been deleted, then AC will show everything in the 3D window.
Selections are also useful for viewing specific things in 3D.
Hope that hasn't complicated matters!
Cheers,
Link.