steam requires many things so it's not recommended for new people. I think you uploaded in HTML5 which is for browsers, it should work on all browsers unless it is super old. So anyway, to get html5 games to play, you will need to have the html file inside the zip with all other files.
Do not make a file in a file, you just need to move the html and the files it needs to zip. It should look like this:
index.html is the main game that itch.io will auto make to the game in your page. Everything else like music, code, images go in a file.
To make your game public you press public on the very bottom of the "Visibility & access" and then" publish" or "save".