Although, i would agree with it not necessarily being "friendly", since its a drastically different syntax than many beginners would be used to, the brackets and parenthesis here are not what you think they are.
Unison is a language in the style of Haskell, F#, Purescript, Elm, etc. So that first line is actually type annotations.
In Haskell, this would just be helloWorld :: IO () , meaning a function named "helloWorld" with no arguments and produces what is essentally a potentially-unsafe IO action with a Void return (the empty parenthesis () ).
Here in Unison they call the bracket part "abilities" or something. Its saying the same thing as Haskell, but being more explicit in saying it can raise an exception.