Among other things, the locator helps you get to a location. Suppose someone tells you that the loot you were looking for just dropped at -250, 10, -120. You can use the Locator to help you get there before it rots:
In this example the Locator shows that the loot is NE (NorthEast) of you. Much of the time that's all you need to know, but the Locator does tell you more. It shows that the loot is 217.48 units away. With experience this gives you a good idea of how far to go. Lastly, the Locator shows that the loot is 56.81 units above you in elevation. In a dungeon this would be critical because it would mean you are on the wrong level and need to go up.
Continuing with the example, you head NE to get your loot. How do you know when you are getting close, and what if there is an obstacle you have to go around? Simply type /loc in-game and the directions are automatically updated using your current position. As you get closer just type /loc once in a while and it will lead you right to the loot.
Using the Locator
All you have to do is set your "From" and "To" locations. You can tell the Locator to give directions from or to you by selecting "(my most recent location)" for the appropriate one. This just tells the Locator to use your most recent in-game /loc command as the location. You then paste or type in the numbers of the other location. You can press to swap the "From" and "To" locations, which will reverse the displayed directions.
Depending on how you set the locations you will do one of the following:
From you to a location - Leads you to a location.
From a location to you - Tell someone how to get to you.
From one location to another location - Tell someone how to get to a location.
The directions are displayed in the Locator window and in the Alert window. The distance and elevation are in the same units as the /loc command.
EverQuest - You only have to enter the first two numbers of a location if you don't care about elevation. EverQuest II - Enter all three numbers of a location because of the strange coordinate system in EQ2.