To run Haku you'll need to install the Raku programming language. If you plan to use Raku (it is a wonderful language), I recommend you use the Rakubrew installation tool.
I am assuming you'll run Haku on command line, in the directory cloned from Git or where you unzipped the downloaded archive.
In that directory is a script haku. Example programs are in the subdirectory examples (horizontal writing) and examples/tategaki (vertical writing).
The first time you run haku will take quite a long time (several minutes) because Raku needs to compile the modules to bytecode. After that, it should only take a few seconds.
Katakana is for variables, kanji for functions and keywords, hiragana for keywords and verb endings (e.g. in 掛ける and 見せる).
This roughly reads as "as for RAMUDA, with a given X it is X times X", so RAMUDA binds to a lambda function. In Scheme this becomes: