Issues with Github. Why is my data not being saved?

Question

GitHub

There is a site repository on Github. The site itself is on Github Pages. Today I made changes to one file of the site through the browser. As a result, everything was saved on the site, but I don’t see the result on my own site. Is it because of local files? That is, I can only change local files from the computer and see the changes on the site? If so, how can I return the files to their original state, like the local ones. That is, how to cancel my changes through the browser. I have been using Github recently, so please do not throw your slippers.