The Graveyard is one of the two instance portals here that isn't behind a great big door. If you go inside of one and it says "The Library!" then you're not in the Graveyard. That would be... the Library. Fight your way through the dungeon, it's pretty linear so I won't explain how anything goes, but at the end you'll fight Bloodmage Thalnos. Killing him is what spawns Scorn, so you will need to clear both of the bosses. You don't need to clear all of the undead in the instance, just clear what you need to so you have room to move around.
While you're clearing, keep an eye out for the Graveyard's rare spawns for extra loot! If you want to use a simple /target Mob command or macro, their names are Azshir the Sleepless, Ironspine, and the Fallen Champion. No 'the' on his name, it's just Fallen Champion.
After Bloodmage Thalnos is dead, run back the way you came, toward the entrance/exit. You'll see Scorn eventually. He's a lich, you won't miss him. He'll be the big undead boney skirty floaty guy.
Scorn is, for the most part, a Frost Mage that hacks and also specced into Mind Flay. He has a Frostbolt Volley, which is an AOE Frostbolt. He has Frost Nova, which is an AOE snare/root. He has a normal melee attack, which he seems to use while Mind Flaying, and he also has one final, ultimate ability. Lich Slap. Ouch!
He doesn't have a lot of HP, so you shouldn't have too much trouble killing him. If casters and healers stand as far away from him as your spells allow, you won't get hit by his AOE spells at all.
Once he's dead, split up your loot! Warriors and Paladins will likely enjoy The Frozen Clutch, a pair of Mail DPS gloves. Hunters might like them as well, but they can't use them until 10 levels after the item's minimum level, so they'll likely find better. Casters and Healers of all flavors will like his other drops. A spell power necklace, Scorn's Icy Choker, and a spell power dagger, Scorn's Focal Dagger.
Again, these drops may not look like much to us level 70 players, but stats like raw attack power and spell power aren't exactly plentiful at these lower levels. These are very good items for their level, and they'll only be around for a limited time.
That's it for Scorn! If you're looking for another target, the closest in terms of level is Lady Falther'ess all the way in Razorfen Downs. Geographically the closest target is probably Lord Blackwood in Scholomance or Balzaphon in Stratholme. Go! Adventure!