It's basically The Sims with less interaction. You create Miis (either via ingame creation or exporting them from the Wii or the previous Tomodachi game), decide on their personallity via sliders and place them in the game environement. You have a limited degree of control over the Miis (mostly by giving them objects, which may effect their mood or what they decide to do, like if they want to go on an honeymoon or something) and most of the game is watching weird shit happen.