How do you make multiple pages in 1 repository?

I’m planning to do more pages for my site and i see other people making multiple pages for 1 site in 1 repository

how do i do it?

From the docs:

You can add more pages to your site by creating more new files. Each file will be available on your site in the same directory structure as your publishing source. For example, if the publishing source for your project site is the gh-pages branch, and you create a new file called /about/ on the gh-pages branch, the file will be available at https://<user><repository>/about/contact-us.html .