The Input / Output section is used to primarily define the channel/universe configurations of each hardware controller connected to the FPP. It is described before the other menu items, becuase it is the first thing that has to be completed.
Clicking on the Input/Output Setup tab causes a drop down menu to be displayed:
The footer of each screen provides an option to shutdown or reboot the PI. You can also restart the FPPD, which is often required to refresh in memory configurations.