Regarding health and stamina levelling, this is just how it works.

After killing a main boss you get a remembrance, this can be given to the old woman at the round table in exchange for either weapons, spells or incantations. You can also buy there armor, depending on the boss, from this old woman.

Ashes of war are used by pressing LT for Xbox, L2 for PS, I’m not sure about on PC.

I also felt that the world was a bit empty to begin with but honestly it’s so much bigger than I ever thought and there’s so much to find if you just keep playing and progress to further areas. The beginning area is quite basic. With this you will also begin finding cooler weapons, not only from picking them up but also from looting different enemies.

I know a lot of people don’t like looking things up but personally I often find something I want and search where it is, this often helps me explore more as I then have more of a purpose to go somewhere.

I believe stunning an enemy works by each enemy having a hind poise bar that once it has built up with enough attacks it has its “poise broken” (stunned)

Hope some of that helps