I know how stupid this question is but i'm brand new to the older games (and to this site), and I need some help with the basics. I'm on the prologue (I think?) and I just defeated a boss in the castle at Jungby. But.... i don't know how to seize the castle. And there's another guy named Gerrar in a castle across the river, which none of my units can cross. How do I proceed from here?