This is how generally an SSL (Secure Sockets Layer) certificate works to secure the communication between the user and the server on a website like this blog site. Image source: Internetum
I have been blogging on WordPress.com site since 2007 (earlier since 2005 in Blogger.com) and since it is a free site where certain things cannot be done or limited (like installing plugins, monetization of the site, etc), all I had to worry about back then was ensuring that I had good content for the blog post. Image source: WordPress.org.
Seriously back then terminologies like SEO, AMP, Fast Website Loading, Caching, Backups, etc was basically sounded alien to me. Well not true exactly, I had some idea on some of the concepts as I have seen the same at my workplace but it was clear that using the free WordPress.com site, there was nothing much I could play around on this.