Can't join a world with my friend through multiplayer. Also I can not turn on multiplayer on my world

My friend can not join my world and I can not join theirs. I also have tried to turn on multiplayer on my world but it's not avalible to change that I guess. Me and my friend have tried everyday for several weeks now and we can not make it work. I bought the game for me and her and I would really hate for my money to go to waste