Notation

Application os denoted by juxtaposition: $(f x)$, for example. In order to avoid writing too many brackets the convention is such that we should not write outermost brackets. Haskell's typical evaluation order will prioritise the application before other operations:

square 3 + 1
-- Is equivalent to...
(square 3) + 1

Application will also associate to the left:

square square 3
-- means
(square square) 3