When the battle starts, the Stormcloaks will attack from below. They will attack the barriers and then the drawbridge. You need to try to keep them from doing this. As you kill Stormcloaks, you will notice a counter at the top of the screen informing you of how much of the attacking force remains.
I highly recommend using magic in this encounter. It will allow you to more quickly deal the enemies and they are moderately armored. You also have many allies who will soak up damage. More importantly, they will draw the attention of your enemies so that they will not run directly away from you.When all of the enemies are dead, report to the General to finish the quest.
