that means that u could use his home as yours, but that phrase is just to make feel comfortable the other person who is doing the visit, cause many times visitors missunderstood that and anyway make hosts feel bad cause of theirs habits, its just a polite phrase in spanish for visitors, also visitors can take this as if they are able to do whatever, so you have to be careful when u say other persons u need to know them first.

my house is you house like welcome

my house is your house

HOLA

my house your house