Let's make a minor change to am existing web page.
This is simple page as it appears in a browser such as Microsoft Internet Explorer:

You change the appearance of text by using HTML (Hypertext Markup Language) "Tags".
In the box below, type the opening bold tag -- <B> -- before the phrase "Generate Source." Type the closing bold tag -- </B> -- after that phrase. The text should look like this:
To make changes to this sample webpage, add tags to this text and click the buttom marked <B>"Generate Source."</B> You'll see the revised HTML in the second text box. To view the revised page in a browser, click on the "View Web Page" button.