Start here:
Creating a GitHub Pages site with Jekyll
Initialize site
jekyll new --skip-bundle .
Use github pages
# Gemfile
# gem "jekyll", "~> 4.2.2"
gem "github-pages", group: :jekyll_plugins
Jekyll and Ruby 3 have a weird interaction where you need to add webrick yourself
bundle add webrick
Install gems
bundle install
Serve jekyll
bundle exec jekyll serve
Serve jekyll with dev config
bundle exec jekyll serve -w --config _config.yml,_config-dev.yml
Syntax highlighting help here