HTML and HTTP are used with the world wide web and the Internet.
HTML is the language that web pages are written in that you view on the Internet. HTML is an acronym for Hypertext Markup language. The pages are written in HTML which tells how the pages are to look which is why it is a markup language. Many pages contain links to other pages which are hyper links with text you see. There are other languages used to do some specialized items on the Internet but most are inside HTML pages.
HTTP is the protocol the Internet uses to talk between two computers when one has a web page the other machine wants to display. HTTP is an acronym for Hyper Text Transfer Protocol. A protocol sets rules on how communications occur between two machines so they both understand each other and transfer the message (in this case the web page) correctly.
HTML and HTTP allow us to use web pages on the Internet and for these pages to be stored anywhere in the world and the viewer to also be anywhere.
You see HTM or HTML as the extension on the web page names which is the last name like Word documents end in .doc or .docx
HTTP appears before the address in the address bar but does not always appear as it is assumed. If you wanted to go to my web page you could type in www.dwightwatt.com, but what is actually used by the browser is http://www.dwightwatt.com
HTTPS is a specialized HTTP. It is secure HTTP and is used for encrypting the message between your machine and the server. You will either see https in the address bar and/or see a little lock on your browser locked which says the communication is secure.