When you go on a visit to the home of a friend or family member, and you are told to make yourself comfortable, that is not the time to go around the house, from kitchen to room and library and generally just checking around the house.
That definitely is not a wise thing to do. The worse thing to do after moving around is to take a book or film from the collection in the library without telling the host and having the intention of returning it. That is considered stealing.
Courtesy demands that you seek the permission of the host to do anything regardless of the fact that you were asked to make yourself comfortable.