seems you just copied the lines somewhere and don't know what f means here.
well, it should be a pure funtion object, please reference to ref/Function
CloudDeploy[
FormFunction[{"basis" -> <|"Interpreter" -> "Number", "Input" :> 3|>,
"exponent" -> <|"Interpreter" -> "Number", "Input" :> 2|>},
#basis^#exponent &,
AppearanceRules -> <|"Title" -> "demo power function",
"Description" -> "Enter two number as prompted below"|>,
FormTheme -> "Red"]]
good luck.