This is a Quarto website; see the Quarto docs for instructions on how to set it up.
Main website content is stored in *.qmd files in the base directory
I suggest using RStudio and the Render Website / Preview Website buttons in it, but you can also use Quarto from the command line. You can render the site with:
quarto render
Or render and serve locally with:
quarto serve
The website is re-rendered and deployed automatically via a Github Action, so you should (in theory) be able to edit the .qmd files directly (even via the Github editing interface) and the website will update when you commit to the main branch.