On the minimap, you may have noticed a lighter grey in some areas and darker grey in some areas. This shows elevation; white being the highest (ex. mountains, hills) and black being the lowest (ex. oceans, pits). The arrow is you; the direction the pointy thing is pointing in the minimap is the direction your character is facing. ^^ In the future, you'll notice that the colored dots on the minimap are your friends. ^^
Public maps are the maps that are automatically installed when you download the game, and private maps are the ones you have to download manually. And someone told you Atlantis was a private map? No, it's public. That person was probably a "territory claimer", and the next time that happens, give them the classic "this is a public map so I can sit here if I want to" speech.
If you're still confused about getting around and stuff, I'd be happy to show you around the game. My in-game username is Kikiorylandia (just like my forum nickname ^^), hope to see you soon!