The raven tells you the game plot. In a nutshell, you work a zone (eg, meadows) until you can defeat its boss safely and move on to the next one. The bosses have offended odin or thor or something and you were hauled here in your afterlife to put them in their place.
Game isn't done, but you can kill bosses in the meadows, black forest, swamp, mountain, plains, and mistlands. Each one is significantly more difficult than the last.
That expands to learning to make new food/gear with new materials in each area and learning how to deal with each new enemy type. Also a key part is base building, which is a mix of function (you must have a base to craft and make progress) and beauty (some people spend months on an exotic base).
Bases can be attacked and destroyed when you are near them, so it is worth some time to learn how to prevent that using raised/lowered terrain or other techniques.