When you save a deck as a ".html" file, it's just a document sitting on your computer. If you want other people to be able to access it from their own computers, you'll probably want to upload it somewhere.
One option is to create a page for your deck here on Itch.io. They have documentation describing how to embed an HTML5 game (in this case, your .html deck) on an Itch project page.
Another option is to use a web host like neocities. You can create a whole website of your very own, for free!
And of course, you don't necessarily have to put a deck on the web at all to share it. You could email the .html file to your friends, or even write it to a floppy disk and physically mail it to somebody as a surprise. Anyone with a reasonably modern web browser can open a decker .html file on their own computer.
Does that help clear things up?
