Approach codes are a pair of Degree and Distance numbers like, 210d100m, for 210 degrees (true) and 100 meters distance. These codes are referenced off the geocache location waypoint coordinates.
These DegreeDistance approach codes describe a waypoint from where you should approach the cache. If you have the geocache waypoint set in as the GOTO waypoint in your GPS then you will be at the approach code waypoint when your navigation screen reads the same Bearing degrees (true), and Distance to the cache as the approach code described. Using this scheme you can find this auxiliary waypoint while still keeping your GPS focused on the goal.
You can have a Series of Approach Codes like 63d600m,330d300m,5d20m to describe a route to the cache that avoids bushwacking and cutting across switch back trails. On a switch back trail your GPS would indicate your closest approach to the cache being straight uphill. Please do not climb straight uphill toward a cache, the trampled vegetation will eventually turn to a washout gully as rain runs down your path.
If you desire, Approach Codes may be converted to actual waypoints in your GPS by using your Waypoint Projection capability. Simply subtract 180 degrees from the approach code, reference the cache waypoint, and project the approach code waypoint. I bet you haven't done this before on you GPS...