HTML is web language, we call it Hypertext Markup language.
HTML is use to create or build a web page (electronic documents), all these web pages that have been created and link to each others with hyperlinks and displayed on the internet WWW - World Wide Web.
HTML similar to digital document (Microsoft Word) , It allows the user (web designer and web developer) to organize and format documents like paragraphs and headings, change the front type and size, insert images etc.
You can use Microsoft Windows Notepad or any other text editor to create HTML file. All you need to do is save the html file with file extension with .html
HTML is a computer language devised to allow website creation. These
websites can then be viewed by anyone else connected to the Internet.
HTML5 is the latest and most enhanced version of HTML.
How to learn the HTML code.
You can buy a book
Creating Web Pages For Dummies, 9th Edition
Bud E. Smith
or get html tutorial online free