Discover is an action performed by pressing the appropriate button when available.
Approach an unknown location Point of Interest and press the appropriate button to use Intelligence or Senses. Hover over the point of interest and the Discover action will appear. Press the appropriate button and a cut-scene will take place showing the name of the new location and a small video flying overhead showing the area you have just discovered.
After discovering the location, while still in intelligence or senses, you can then Memorize the point of interest so you can investigate it. Once a location has been memorized, you can Remember or Forget the location.
Discover is the location equivalent of the Inspect action.