Make yourself at home

To make yourself at home means to behave in a relaxed and comfortable way in someone else's place, as if it were your own.

The phrase has been used for a long time as a friendly way for hosts to welcome guests. By telling someone to make themselves at home, the host shows that the visitor is welcome and should feel comfortable there.

The neighbour's cat wandered in through the dog door, jumped onto the couch, and immediately made itself at home.