Can you get to a dungeon without having visited the area it is in before?
Like AC shows on my game map but I have not been to that area yet.
Can I do AC yet and if so how?
Thanks in advance! 
Getting to dungeons
First off, I’ll explain why you see it on the map. When you get to the relevant levels (AC is level 30 for story mode, for example), you will get mail from an NPC, telling you that a dungeon is available, which includes a “show me” option. Even if you delete the mail, the dungeon icons will show on the map as long as you meet it’s recommended minimum level.
The recommended levels are on this wiki page: http://wiki.guildwars2.com/wiki/Dungeon
Even if you have not been to the dungeon’s zone map, you can still access the dungeon. One easy way is to have one of your party members start the dungeon instance. When they are inside, you will get a prompt as long as you are in or whenever you arrive at the dungeon’s zone map. If this is not an option, you can always walk to the indicated dungeon location on your map.
Short version:
If you see the dungeon’s map icon, at the very least, you can enter that dungeon’s story mode.