Continue out of the room to reach the ramparts themselves. The door on the right is a shortcut you will want to open in a bit, to get back through, so continue to the left. The white enemies ahead are called Envoys, and you can find them in a few locations throughout the capital....
I'm not here to give you a full-blown boss walkthrough, as there are plenty to be found all across the internet. But the plain fact is that this fight is hard. One of the beautiful things about Elden Ring is how many ways there are to give yourself an edge in various challenges. ...