OSTAGAR
Is a ruined fortress in southern Ferelden, on the edge of the Korcari Wilds. Representing the furthest point of encroachment by the ancient Tevinter Imperium into the barbarian lands of the southeast, the fortress was once one of the most important defensive Imperial holdings south of the Waking Sea.
This quest will begin once you've ended one of six available origin stories. The first person you'll meet in Ostagar is going to be King Cailan and you won't have to be too kind for him, because you won't receive any penalties for being rude. Duncan (Ostagar M1, 1) will inform you that you'll have to take part in a ritual to become of the Grey Wardens.
Once you've arrived at the northern ruins find Alistair and approach him (Ostagar M1, 3). Wait for Alistair to end a conversation with one of the mages and then you'll be allowed to talk to him and to confirm that you want to take part in the ritual. During the conversation you'll find out about two other recruits (Jory and Daveth) whom you've might have already met and they're are also going to take part in the preparations for the ritual. Once you're done talking open a chest located close to Alistair to collect valuable runes.
Alistair
We always recommending exploring around Ostagar to find some herbs, along with meeting other characters to get more information for the codex, such characters being Ash Warrior Leader, Kennel Master, Quartermaster, and Wynn.
Ash Warrior Leader
Jory
Kennel Master
Elven Messenger
King Cailan
Notice that your ally has given you a few basic pieces of equipment and it would be a good idea to examine them in your inventory. Follow Duncan's instructions by heading west and crossing the large bridge. You can now talk to Duncan again (Ostagar M1, 2) or proceed directly to the north.
Daveth
Quartermaster
Wynn
There are other NPCs around that can give you quests or rewards, like the Elven Messenger and the Hungry Prisoner. Otherwise you can return with Alistair to Duncan (OstagarM1, 2).
The Hungry Prisoner
Talk to Duncan to find out that before taking the ritual you'll have to perform two impotant tasks. Your objectives will be to deliver three vials of darkspawn blood and to locate an area where Grey Warden's archive documents are being stashed. Ask additional questions about each task if you want to and after the conversation head west. Talk to one of the guards to let you through to Korcari wilds (Korcari Wilds M1, 4), where you proceed to complete the two quests, Tainted Blood and The Grey Warden's Cache.
If you want to complete side quests before leaving to the Kocari Wilds, here are the ones we recommend to do.