You have to deploy a cooking pot, and use food on it.
You refill cup by dragging an empty cup on a filled barrel, if I remind well.
As for your other questions, get ready for some major disappointment (so far) if you expect DOS to be even vaguely interactive in this matter(It seems interaction means breaking/moving/opening barrels/crates/fish stacks around.
Even if the beta has some huge improvements, it seems DOS is not the game I was expecting, world interactions and depth wise.
I thought I would find a golden statue, but once you scratch the paint, it's a block of bricks. My bad, I was, as always, to entusiastic.
So, inquiring mind, get ready to learn everythings there are to learn about interactions in about 30 sec...
