It doesn’t come as easy, as you might think, to be a guest. You are being hosted for one of two reasons: they thought you would be interesting to have around with whatever skills and stories you said you had, or, they felt the need to help you out since you had nowhere else to go. Either way you are expected to act like a guest in their home, and to be fun and interesting. Don’t take anything for granted and generally be nice.
It is super impolite to not hangout with your host. This doesn’t mean you are trapped with them, just that you need to spend time with the person who is being so kind. Generally they will have work or something and you can explore during the day, but a lot of times you end up having an immediate friend-type relationship with them and you don’t want to be without them. What you think of being with your host differs time to time.
Little perks that a lot of hosts give you, a key to the flat, freedom to raid the fridge, not caring how late you come back etc, should not be expected or taken for granted. Always accept graciously whatever it is they give you, you are getting it for free unless you forgot.