Routing rules are configured independently of folders and channels, which means that a routing rule can easily be applied to a number of channels after it has been made. It also implies that if you only want to make a small change in any of your routing rules, all affected channels are updated accordingly.
Go to the Routings tab at the top of the configuration screen and click on the green Plus icon at the bottom of the list of configured routing rules. If you create many routing rules and wish to group them for a better overview the two other buttons will let you create groups and name them.