What are Github Project Pages and how to use them?

I am confused about Github "project pages". How are they different from the "user pages"?

I am using Github Pages for my personal website with custom domain. I'd like to add another site to it like this http://serhii-css.com/my-other-website, like another repository. Is it possible?

Thank you.

Solution

I finally figured this out.

Got to github.com
Create a new repository (for example "new-project")
Got to the setting of this repository
In the "Github Pages" section make sure to have "master branch" or "gh-pages" selected under "Source"
Now your new repository will be available at http(s)://<username>.github.io/new-project