The Special Characters window allows you to insert high-numbered ASCII characters which normally won't display in the browser unless you provide special codes. These are especially useful when describing HTML tags or writing foreign characters. You can make the Special Characters window appear by checking the Special Characters menu option on the View menu.
For instance, say you want to put <HTML> in your text and describe its attributes. You cannot simply type <HTML> in your text because the browser will interpret that as a tag. Therefore, you must type in <HTML> The < puts a less-than symbol in its place and the > puts a greater-than symbol in its place, thus allowing you to print the tag in the browser's display.
If you are writing a document involving foreign characters such as an e accent grave, you cannot put the character in the document source. In order for it to display, you must type è into the document source.
To insert a special character using the Special Characters window, simply move the mouse over the special character you'd like to insert and click on it.