Add the exit with the given object number as a conventional exit from the current room (that is, an exit that can be invoked simply by typing its name, like 'east'). Usually, @dig does this for you, but it doesn't if you don't own the room in question. Instead, it tells you the object number of the new exit and you have to find the owner of the room and get them to use the @add-exit command to link it up.