`f :: Int→Int→Int`, f is a function that takes two `Int`s and returns an `Int`, that’s the short story.
Reading type signatures is the first step to understanding what a function does or how a complex program is composed together. It took me some time to get my head around them and I have seen people struggle with them, especially developers coming from dynamic languages. Even for developers from strongly typed languages like Java they are alien. The text makes them more accessible. My recommendation would be to plough through it without accessing the references in footnotes and then re-read it more slowly with references. If something is still unclear or could be improved - do reach out (@ppurang).