Don’t send the HTML link, since that link will only work on your own computer.
Instead, you should ZIP up the saved/published HTML file and any other files that it needs to work (images, etc.), and then either email that ZIP file to them (if it’s a small file) or put the ZIP file online and email a link so they can download it. If you want a free place to do temporary uploads, use the “link” method at ShareGB (or some similar file sharing platform) to generate a temporary download link to the ZIP file. If you would prefer a more permanent link, then you could upload the ZIP file to Google Drive, mark the file as shared, and then give them the link to download it from there.
Alternately, you could host the HTML file online. A free method to do this would be to upload the file to Google Drive and then enable sharing on the HTML file. If the HTML file needs other files, such as images, then they’ll need to be uploaded there and have sharing enabled for them as well. Next, set up a DriveToWeb account, and that will then allow you to share a working link to the game in your Google Drive so that others can use that link to play the game online. (Note: There’s a monthly download limit from Google Drive, so don’t use this method for games with tons of images, sounds, and videos, or games that will be shared with thousands of people. For your purposes, this limitation probably won’t be an issue.)
For example, I use Google Drive and DriveToWeb to provide access to my Twine/SugarCube sample code collection, though I also provide a ZIP file download link for it.
Hope that helps!