First, get the prerequisites.
npm install
Next, you simply run the build script.
npm run build
There are some environment variables you can supply that control some settings during build.
# Produce unminified files
UNMINIFIED=true npm run build
# Debug the generation of some files by writing JSON of metadata in build/
JSON="somefile.js folder/another-file.html" npm run build
# Show timing information
DEBUG=metalsmith-timer npm run build