There are two methods of navigation used in the absence of radio navigation aids.
Dead Reckoning and Pilotage.
The two are used together whenever possible.
Dead Reckoning is essentially keeping track of your estimated position mathematically. You are flying known courses at known (hopefully) ground speed. Dead reckoning requires good planning to be reasonably accurate as there are many factors that reduce its accuracy. A few are compass errors, magnetic variation, winds aloft. Simple things can get you in trouble with dead reckoning. You plot your course on the map as a true course (referenced to true north). In order to follow that true course you have to correct for magnetic variation and compass deviation as well as calculate the required wind correction angle. A math error in the planning and you can easily be completely lost.
Pilotage is navigation by reference to visual landmarks.
In good weather over land the two methods are used together. One backs up the other. In poor weather or over water all you have is dead reckoning.
Reckon correctly or you are dead as the joke goes.
In reality even in poor weather or over water there are visual clues as to your location. Cloud formation differ over land in the open ocean etc etc. That is where experience comes in.
