HTML is what a server on the web sends to your web browser for interpretation. To see some HTML right-click your mouse and select the "View Source" or  "View Page Source" menu item.

We will not cover specific HTML tags over here - it is an independent topic.

The following are good places to pick up some HTML:

Complete and official reference
http://www.w3.org/MarkUp/

HTML Tutorial and Reference
http://www.htmlcodetutorial.com/

HTML Fast and Easy for You
http://www.htmlgoodies.com/primers/html/