Well, you need another Map first of course. Then yes, you go to the third column and type in the Map name you want to put in. Then press "New" (I think that's what it says) and it should pop up with your mouse.
If it doesn't, make sure you're:
- Camera is in the Map, not looking at it while floating in nowhere.
- Wait a minute at least. It might take a second or two to load.
- Make sure the Map Name is correct.
- If it doesn't load, save the Map and exit out and then try it again. Remember to SAVE any unsaved sturf.