As battles in the Abyss differ greatly from those in Atreia, there were several things you needed to learn. You visited several instructors to learn about fortresses and capturing a fortress, the Aetheric Field surrounding each fortress, the Castle Gates and Gate Restoration Stone, the Guardian General, the Artefacts, Kisks, and the Balaur Battleship known as the Dredgion. When you returned to Claudia after completing all the lessons, she gave you a Kisk Stone, to help you during your travels in Reshanta.