The BR tag is used to make line breaks within text. Most of the time these line breaks are simply a space between lines by browsers, except when inside the PRE tag.
The CLEAR attribute is optional and is used when you have an IMG image in your text. If that image uses the ALIGN=LEFT or ALIGN=RIGHT tags, then the text will flow around it. If you have text that you want to appear below the image, you can do this with <BR CLEAR=LEFT> or <BR CLEAR=RIGHT to force scrolling down to a clear left or right margin, depending on the tag used. Using the CLEAR=ALL tag will scroll down until both of the margins are clear. CLEAR=NONE is the default of this option, and does nothing.
Sometimes the use of multiple BR tags will force several lines of whitespace, but this is not supported by every browser.
This code is an example of the BR tag, it makes a <BR>space like the one above.
This is an example <BR><BR><BR><BR><BR>of whitespacing.
Inside of the PRE tag BR shows up differently.
The BR tag can be placed inside the PRE tag