Radio navigation requires that bearings, or directions, of two or more radio stations of known locations, as determined by means of a radio compass, be plotted on a map. The crossing point of two bearings, or the center of a triangle in the case of three bearings that don't all cross at the same point, is considered to be the location of the airplane. This method is the least accurate of all the methods, because the bearings can be bent by air or thermal conditions, coastlines, or even deliberately bent magnetically. Once during WWII, the Germans bent the bearing of radio stations that were being used by a squadron of American planes returning to England from a raid and the planes ended up, tragically, over a nest of anti-aircraft guns. Radio bearings have probably never been used for wartime navigation since.
Celestial navigation is the most sophisticated of the methods.
An instrument called a sextant, or octant, depending on its configuration, is used to determine the angular elevation of a known bright star or stars. The navigator was required to memorize the identity and location in the sky of 50 stars that might possibly be used for navigation in various parts of the world. The precise locations of the stars in the heavens were tabulated and available to the navigator. To utilize the elevation readings, the navigator would assume the best location of his position that he knew, apply the location information of the star he observed, and calculate how far he was and in what direction from his assumed point. Every feature of these navigation processes were taught and drilled in the classroom and practiced in flight applications.