Enter any piece of HTML code in the space below and push the "Submit" button to try it out and see how it will look! Note that you do not need to enter the <html> or <body> tags. For example, if you enter <h1>Hello!</h1> in the space below, you will see the word "Hello!" in an H1 font when you push the "Submit" button. Have fun!
For a complete introduction to HTML, see How Web Pages Work.
For a one-page HTML cheat sheet see the Big List of HTML Tags.