The same way you'd use a map in real life. You had a compass, so you know which direction you're going. Combine your direction with landmarks and topography, and you're navigating!
I tried to recreate the feeling of this with my mod, Redux, by removing the player indicator from the map. This requires the player to use their GPS + map.
https://www.moddb.com/mods/far-cry-2-redux
Let me know what you are interested in. I've uploaded a Nasreen version (using her model in the video), in which she subs in for Frank.
The animations are not currently included in Redux do to the motion sickness they can cause, but if you want them, I can make a special version.
https://www.amazon.com/Far-Cry-Blutige-Diamanten-Bd/dp/3833217421 i wish it was available . ive been looking everywhere for it , but no luck