Like with most pages in FrontierNav, you can use Universal Search to quickly access what you're looking for. Doing so with the Interactive Maps open will take you to any relevant markers.
LeftClick the "Eye" icon on the bottom left of the map to access the Map Legend in the Sidebar. From there, you can toggle specific types of markers.
Some maps may have too many markers so they'll be hidden by default. You can see how many types of markers are hidden by the number next to the "Eye" icon.
Sometimes you'll want to mark locations of interest that may not be part of the official dataset. A point of interest you want to come back to, a place with good loot, whatever it is.
RightClick on the place you want to place the map note and use the Sidebar to enter some text. The first line will be used as a label for the marker.
To learn more about Editing Maps, read the sections on Editing Data.