GPS provides you with your current coordinates in World of Warcraft. You can then save these coordinates or enter new ones. The data you enter will be shown on the worldmap and on the minimap. It's easy then to track stuff and remember where things are.

Your location

Your current location is shown in a little frame which can be drag/dropped where you want on screen. To achieve this, just click on the figures and drag the frame.

Add new locations in current zone

To see the interface, just click on the compass in the location frame, it will open the management interface. You can then enter a new location by typing its X/Y coordinates as found on other sites (Wowhead or Thottbot for example). You can also focus something with the mouse and click on the small arrow next to the decription field, it will fill your current location with your focused object/NPC coordinates. Then click Save to save what you typed.

This will add a dot in your minimap and on your worldmap. If the location you entered is not close to you, it will be shown with an arrow in the minimap.