Usually a site has many pages, but the index page is the most important, it's the first page you see.
You can simple add a HTML file with a suitable filename in the root of your site. You can also write a page in Markdown using a
.md extension which converts to HTML on build. For a site with a homepage, an about page, and a contact page, here’s what the root directory and associated URLs might look like:
├── about.md # => http://example.com/about.html
├── index.html # => http://example.com/
└── contact.html # => http://example.com/contact.html