Content is currently under development for Setup. When complete you will see a list of all the different documentation sections here that you can go to, with an emphasize on global and sale channel configuration options, along with money center. References will point you to setup in other groups, such as setting up a cash register in point-of-sale. You will also be able to select these from the menu on top.
In the interim, many of the options, fields, and selection lists have context sensitive help that you can view by holding your mouse over the item.