If you mean to get into the instance, it will be in your Instance Join panel under Classic, probably listed as "Angmar: Urugarth"
If you are not yet of appropriate level (say you just turned 45 and picked up your class quest - I am unsure what the minimum level requirement is, but I believe most of the mobs may be level 48?) you will have to get someone who is to start the instance so you can join.
If you mean to find the physical location, you will need to go through the Gate of Shadows (from Gath Forthnir you will go west and north). You will have to have done Volume I Book 7 to get the key. At level, this is very difficult to do alone as there will be many difficult mobs guarding the road and the gate. After going through the gate you will reach the Tarmunn Sursa camp. Across the bridge from TS you will find the physical locations for Urugarth and Carn Dum. If you have not done Volume I Book 7, you can have someone who has open the gate, or there are summoning horns at Tarmunn Sursa or at the portals to Urugarth and Carn Dum themselves to which you can have someone at site summon you.
Last edited by tomiathon; Feb 23 2012 at 03:11 PM.
Also, just in case you want to go to get class quest items, those items are also available through skirmish vendors (curiosity vendor I think), and in some cases also drop from mobs outside Urugarth. If you are f2p, you do not need to purchase angmar to complete your class quest.