You will see icons appear over certain objects, like a door over a surface you can open, or a graphic of a person sitting in a chair. Those icons show you can interact with that object. If you do not see an icon, it means that object is simply decoration.

Chairs – When you click on a chair you will walk over to the chair and sit in it. In order to get up from the chair, just push the forward arrow key and you will stand up.

Doors - Doors must be clicked to walk through them, in the same manner as chairs and other objects.