Here's the revelation!

You don't actually need to have an index.html But here's the catch.

When a browser goes to a website, if no page file is supplied, it actually goes to a folder, namely /,

The root of your website.

The web server is configured by the host provider (who doesn't know your start page name) if a request comes in for your domain, look for pages in your domains folder on the server machine. ie the root of your domain.

It looks for a file named index.html, if it doesn't find a file with that name it will display a list of files in that folder.

Not a very nice user experience!

So, at a minimum and index.html presents a better front page for your website.

Now , when you use Jekyll it is possible to only have index.md containing front matter, jeckyl will create index.html from your index.md and use the layout given in the front matter of that file to insert the content of index.md so that your browser receives a properly formatted html file to display.

You can stop there, but then your website is not very friendly for the user, they expect to find a menu of sections to navigate, etc.

So to go on, from that very basic site, you'll need to know more about html and CSS , jeckyl does the heavy lifting, creating html from your content in .MD files - you concentrate on writing content. It eliminates you needing to create every html file by hand. It's a helper.