Everything through from rules to traction to routes is structured and done in a way so it sinks in. From my experience the first route is the hardest to learn but once you’re into a routine and know what’s expected it becomes easier. When I learned my routes I used to write the key things down and memorise the list then put the location to the name and found that way worked for me.
At my TOC you need to know stations along the route (including ones not stopped at and dispatch arrangements for them in case you unexpectedly terminate etc), viaducts, tunnels (and lengths), junctions (and where they take you), crossings (and type), signal boxes and area
Controlled, type of signalling, direction of lines and if lines are bi directional, line names (up fast, down Normanton etc), OLE/3rd rail areas, station facilities, signals and off indicators, dispatch arrangements (RA/Flags etc).
It sounds a lot to learn but it all falls into place. I was dreading routes but once you do your first and sign it off, you’re in a routing and subsequent routes are
Much easier to learn.