The system is made out of modules from the `modules/` directory. When you run the build script, it assembles them, and optionally optomises the code for space.
There are a number of preconfigured module sets in the `config/` directory, and you can of course you can write your own.
Simply run `build.lua`. Under OpenOS or plan9k that may just be going to the right dir and entering `build`, but under proper UNIX systems it may involve `lua build.lua`.