First of all, install the Tox core library. Follow the toxcore installation instructions.
Next, install Racket through either the repositories or by source.
Now, install the Racket wrapper to libtoxcore by following the installation instructions provided.
After that, install the Racket wrapper to OpenAL by doing the same for libopenal-racket.
Then download Blight itself with git clone https://github.com/lehitoskin/blight.
Then run ./main.rkt to start Blight.