To start your quest dawnguard must have level 10, after you install Dawnguard addon, please speak with one of the big city like Whiterun guard Guard to begin Dawnguard questline.
Start the quest Dawnguard open your quest log
I’ve learned of a group of vampire hunters known as the Dawnguard. It seems a They are looking for new recruits.
Speaking with chairman Dawnguard.
Another way to start this quest is to talk to Durak WHO will come to you, Sometimes after you are attacked by some vampires.
Durak: You there, the Dawnguard is looking for anyone willing to fight against the drawing vampires’ Menace. What do you say?
Your assignment: Find out about the Dawnguard.Your options are:
What’s the Dawnguard?
I have not noticed any vampire Menace
Killing vampires? Where do I sign up?
Sorry, I’m not interested.Skyrim Fort Dawnguard Map
Your destination is Southeast of Riften. Fast Travel to Riften, then travel south east on the road and past a bridge. It is a pretty long walk there, go around the north side of the mountains. If you have a horse it is a good idea to use it for this trip. Go through a cave to Dayspring Canyon.
You run into a torch bearing NPC named Agmaer WHO ACKs you if you are here to join the Dawnguard too. Follow him. Listen to the dialogue, Agmaer also wants to join the Dawnguard and become a vampire hunter. He Tells You That you have probably killed lots of vampires and that ‘Isran will sign you right up.
Skyrim Fort Dawnguard
Soon you arrive at Fort Dawnguard the which is a very big fort. You Might Run Into Durak again on the way. If you talk to him, you can get him to give you a crossbow. Keep Following Fort Agmaer and enter through the main gate Dawnguard. A guard named Celann standing on the stairs in front of the main gate Isran Tells You That Will Decide if you have got what it takes. Enter through the big door.
Your dialog choices are:
I’m here to join the Dawnguard
I heard you were looking for vampire hunters
I was just looking around. What is this place?
Choose the first option. Isran Tells you to look around. There is really not much to join yet. He has only started rebuilding the order. Ask him what you could do to help. He Tells You That he needs someone in the field, taking the fight to the damn vampires, while we are getting back into shape the fort. Talon was telling about some cave Isran That the vigilants were poking around in. Seemed to think it was related to these recent vampire attacks.
Tells you about Dimhollow Tolan Crypt. Brother Adalvald sure it was some long-held last vampire artifact of some kind.
This completes the quest “Dawnguard”, and starts the next quest, “Awakening”.