I think you might need to add the formations menu to your character set. Or you can add a hotkey to one of the formations defined in Base Hotkeys keymap.
Either set a Hotkey for the existing formations in the "Base Hotkeys" Key Map, or, as Wizeowl alluded to, use the "Formations" Menu (although you will likely need to change its Hotkey to something other than default, if you aren't assigning it to your Character Set directly).