I don’t even remember anything in AC6 I would consider a tutorial. Unless he means the first 5 minute mission.
OP, the only multiplayer you missed playing with your sister was pvp, and you would have been absolutely shat on if you went into pvp. And you would shit up the games for other people too, because no one wants to fight a bunch of noobs all in the same starting gear who don’t know how to move (or worse, have them on your team).