It helps if you avoid the syntactic sugar of do-notation:
main = getArgs >>= processData >>= displayData
main is in the IO monad. The >>= function takes a value wrapped in a monad and a function which accepts a value and returns a value wrapped in the same type of monad, and returns the same monad-wrapped value the function did. It can be used as an infix operator because Haskell allows that if you specify precedence, in which case its left side is the first argument (the value-in-a-monad) and its right side is the second argument (the function).
The (imaginary) function getArgs takes no arguments and returns a list of command-line arguments wrapped in an IO monad. The first >>= takes that list and feeds it into the function on its right, processData, which accepts it and returns some other value in an IO monad, which the third >>= accepts and feeds into displayData, which accepts it and returns nothing (or, technically, IO (), the unit (empty) value wrapped in an IO monad) which is main's return value.
See? Everything is still function application, but the mental model becomes feeding data through a pipeline of functions, each of which operates on the data and passes it along.
The (imaginary) function getArgs takes no arguments and returns a list of command-line arguments wrapped in an IO monad. The first >>= takes that list and feeds it into the function on its right, processData, which accepts it and returns some other value in an IO monad, which the third >>= accepts and feeds into displayData, which accepts it and returns nothing (or, technically, IO (), the unit (empty) value wrapped in an IO monad) which is main's return value.
See? Everything is still function application, but the mental model becomes feeding data through a pipeline of functions, each of which operates on the data and passes it along.