To play it, just get the .HTML file from the button above that says Code and run it from there, or just make your own .html file and copy and paste it.
This was a quick and fun project that was made by me (1OTH3R) and is my second project ever posted on GitHub. Alternatively, go to https://1oth3r.github.io/3D-HTML-Game/ if it isn't blocked by any school restrictions.
Small edit: I have unpublished this from GitHub pages, as I do not want 1OTH3R.com to be flagged as a games site on some devices. For now, use the steps above and just use the HTML file itself.
Have fun!