HTML is the building block each website is created with. It is a series of elements called tags and angle brackets " " all buried with the contents of the page.
Web browsers analyze the tags to interpret the content of the web page, blog, etc.
HTML is also what allows embedded objects and images to display and to be interactive ( click to go to location).Like for blog buttons.
I am not an expert on HTML codes. But, what I don't know I can always research and find out.