The viewfinder ring is for manual focus, of the 'split prism' type. When the subject is in focus, the two halves of the split ring will be in alignment and the split will be difficult to notice.
You are correct about the aperture ring. You can manually set it. The fixed band with the aperture numbers shows DOF for each aperture, and the other moving ring markings are for distance. One set should be in feet and the other in meters. (The '8', is likely sideways, and is the symbol for infinity) Red markings are probably the macro focal distance when 'macro' is engaged. There should be some sort of indicator for exposure settings.
(OK, found this page: http://camerapedia.wikia.com/wiki/Yashica_FX-3
with more info)