I dont know what we mean by open or closed >.>
Open setup is when you know the roles handed out beforehand. Closed you do not.
Open is easier for newer players because you know which roles are in the game and that you can counter-claim someone with more reliability than in a closed setup, where there could easily be two of you with the same role and no one would be the wiser. Closed setup is easier for the mafia because it gives them more wiggle room when it comes to claiming. You can get away with a lot more bullshit in closed than not.