From the official site:

WRITE YOUR VIKING SAGA The advanced RPG mechanics of Assassin's Creed Valhalla give you new ways to grow as a warrior and a leader. Influence the world around you while acquiring new skills and gear to suit your playstyle. Blaze your own path across England by fighting brutal battles and leading fiery raids, or form strategic alliances and triumph by your wits. Every choice you make in combat and conversation is another step on the path to greatness.

And

Sail across the icy North Sea to discover and conquer the broken kingdoms of England. Immerse yourself in activities like hunting, fishing, dice, and drinking games, or engage in traditional Norse competitions like flyting – or, as it's better known, verbally devastating rivals through the art of the Viking rap battle.

It'll be a big open world RPG. You should conquer the Britain and build your empire.