They are Russian 35mm cameras designed and produced from around the 1960's as a cheap copy of the now classic and still very popular German made Leica; both these cameras use the Leica M39 screw mount.
The FED 3 has the 52mm Industar 51 lens and the Zorki 4k is seen with the 35mm Jupiter 12, the Zorki also has a 35mm viewfinder to match the 35mm lens. What you do is focus through the coupled rangefinder/viewfinder on the camera body then compose through the viewfinder on top. It may sound like a handful but it really isn't after a little experience.
Another thing with these cameras, there are no built in light meters. It may sound like a horror story in today's world of auto but they are very versatile cameras and a pleasure to use.