Generally speaking, follow the instructions at

https://docs.github.com/en/pages/setting-up-a-github-pages-site-with-jekyll/testing-your-github-pages-site-locally-with-jekyll#building-your-site-locally

to build the website locally, and run a webserver to inspect your local changes.

Run the following to re-build automatically when your files change:

bundle exec jekyll serve --host 0.0.0.0 --incremental

To duplicate a page from the previous year (let's say 2021), to create a page for the new year (let's say 2022), the following changes are necessary:

1. Copy the static files with cp -r 2021/ 2022/
2. Copy the layout file with cp _layouts/layout_2021.html _layouts/layout_2022.html
3. Make copies of _includes/head_2021.html, _includes/header_2021.html, and _includes/footer_2021.html
4. Add entry button for new year in _includes/header_common.html
5. Copy the main content file with cp _pages/home_2021.md _pages/home_2022.md
6. Edit the top lines in _pages/home_2022.md such that the new year is reflected, the new files are used, and the new page is actually generated by Jekyll.
7. Edit index.html to refresh to the new page.