After successfully recruiting Sorine Jurand and Gunmar, you return to Fort Dawnguard. Both new recruits are standing in the main court. Join them. Isran fills the chamber with some sort of mist, some sort of test to make sure that none of you is a vampire.

Isran briefs you and the rest about the situation. You are up against powerful vampires, and they have an Elder Scroll. If any one is going to stand in their way, it's going to be us. Sorine asks what we know about them and what to do now. Isran instructs Sorine to start her tinkering on the crossbow design she has been working on. Gunmar is given an area large enough to pen up some trolls, get them armored up and ready for use. In the meantime, Isran wants to have a little chat with you as to why a vampire showed up in Fort Dawnguard looking for you.

This completes the quest "A New Order", and starts the quest "Prophet".

You can talk to Sorine Jurand. She is an archery trainer, so she can train you in the archery skill if you need. You can also ask her if she can teach you how to make a crossbow, and she says that if you know anything about steel smithing, it is pretty simple, and to talk to Gunmar if you need materials. You can also check what she has for sale, mostly some steel bolts and potions.

Gunmar is a smithing trainer. Talk to him to train in smithing. You can also buy an armored troll from him, for 500 gold. The troll will act as your pet, following you around and fighting with you. But Gunmar warns you that the troll is no pet. Mistreat the beat or leave him alone for too long, and he'll return to the wild forgetting you ever existed. You can also check what Gunmar has for sale. He has a large bariety of weapons, nothing too good though.

Skyrim Dawnguard Armored Frost Troll Follower

When you are done talking to Gunmar and Sorine, find Isran on the top of the fort and talk to him. You can ask him about the old Dawnguard, and learn that back in the second era, the Jarl of Riften had a son. Adventurous type, too much for his own good it seems. Wound up turning into a vampire. The Jarl, unable to kill his own son, spent a fortune building this keep and hiring men to guard it. Their job was to keep the Jarl's son contained within. They took it seriously, and served honorably. They were eventually forced to put him down. The Jarl banished them from the hold, but they stuck to their cause. Fough vampires wherever they found them. Isran aims to continue that mission.