Well I don’t fly 72s anymore, not for the last six years anyway, but I did fly 72s with long-range navs back then. We had INS (the chief pilot didn’t believe in GPS, go figure) and to give you a simple answer one just put the waypoint into the INS, by name on the newer INSs or Lat. & Long. on the older ones and then coupled the autopilot and the INS would take you to the waypoint.
On the older INSs we only had 9 waypoints and when flying in South and Central America before they got enroute ATC radar we would wear out our fingers typing the lats and longs into the boxes.
Ah, automation!