naming pages with .html extensions

Hi:
Just starting to use WP as a platform for site building. Have been building static html/CSS sites and want the dynamic functionality and CMS capabilities of WP. But have to make some adjustments and one is the page naming. I’m used to simple urls like https://www.mysite.com/index.html, or aboutus.html, etc. I want to retain my google equity (for my site and client sites) so I want to be able to keep page names as much as possible. I’ve read that I need to use the Permalinks feature for page naming – how do I get it to create .html page names?

Thanks!