The “docs” folder on GitHub is special: if your project is set up to allow it, any files in this folder will appear as a GitHub Pages website. For example, this template is located at https://github.com/djnavarro/newproject, and because I have enabled GitHub pages for this project all the files in this folder are hosted at https://djnavarro.github.io/newproject. It is very often useful to have a public facing website associated with a project that gives people an overview of the whole thing, and this is an easy way to do it.
To help you get started, GitHub have a nice walkthrough showing you how to enable GitHub Pages for a specific project. There is als a more detailed tutorial here