As always it does depend a bit upon context, but normally it means something like "you can go out". For example I have a pet rabbit who is sometimes allowed to hop freely around the living room. When I open his cage I sometimes say "out you go". It is giving him permission and encouraging him to get out of his cage, but falls short of the blunt order "Get out!". In some contexts, however, it could be used to convey the meaning "Go away!" but in a less abrupt and slightly more polite way.

It is more like, "Go outside". A mother could say to her children,"Out you go," when it is time for the children to play outside for a while.