What it is
A setup is basically adding a large gathering of roles and putting them into one "setup" so they can be played in games that you "sit down" in. Setups must be balanced or else they cannot be made. Some roles are restricted in certain lobbies so use what you can if you are restricted in a lobby currently. Every setup is unique and some people spend a lot of time making setups so when you make a setup, try to make the best one you can.
Point Distribution and the setups
Setups give you points according to the setup statistics which are calculated every time a ranked or competitive game is played on that setup. During the first 50 games of playing ranked or competitive of that setup, it will give you a base point amount of 60 points but after that it will give you points according to the win percentage of that specific alignment.