Refer these for help:

• https://docs.github.com/en/pages/setting-up-a-github-pages-site-with-jekyll/adding-content-to-your-github-pages-site-using-jekyll
• https://docs.github.com/en/pages/setting-up-a-github-pages-site-with-jekyll/adding-a-theme-to-your-github-pages-site-using-jekyll
• https://docs.github.com/en/pages/getting-started-with-github-pages/configuring-a-publishing-source-for-your-github-pages-site