In Haskell, all functions take one argument. Also, operators are functions.

First, the one argument thing is known as currying. With higher-order functions, returning a function is admissible, so

    map :: (a -> b) -> [a] -> [b]

can also be thought of as:

    map :: (a -> b) -> ([a] -> [b])

like so:

    ghci> :t map length
    map length :: [[a]] -> [Int]

As for operators being functions, function names that are alphanumeric default to prefix (e.g. f 10) while those that are symbolic default to infix (e.g. 10 + 18). To use an alphanumeric name in infix, use backticks, e.g.:

    ghci> 5 `max` 6
    6

Use parentheses to prefix an "operator"-style name, like so:

    ghci> (+) 5 6
    11

The (+1) that you're meeting is an additional bit of syntactic sugar. It's identical to (\x -> x + 1). It allows you to do things like this:

    ghci> map (2^) [1..5]
    [2,4,8,16,32]
    ghci> map (^2) [1..5]
    [1,4,9,16,25]