the <br> tag

The line break tag <br> has been used by itself in the past. To make your html well-formed, it should be closed. Therefore you should write it as: <br />

The attributes

clear          left, right or all
               Example: <br clear="left" />
               the line will break and then 
               restart when there is nothing 
               obstructing the left margin 
               (such as an image)

Example

If I write an address in notepad like this:

<p>Jo Bloggs
24 High Street
Smallville 7890 TAS</p>

It will be displayed like this:

Jo Bloggs 24 High Street Smallville 7890 TAS

To force the line breaks you have to use the <br /> tag. Like this:

<p>Jo Bloggs<br />
24 High Street<br />
Smallville 7890 TAS</p>

... and the result is:

Jo Bloggs
24 High Street
Smallville 7890 TAS