Depending on which DTD (
Document Type Definition) you have in the top of your page determines which style to use.
<br> - Is HTML complaint.
<br /> - Is xHTML complaint
they are stand alone tags, just like the <
hr> tag creates a horizontal line in an HTML page.
example
Code:
<p>YourName<br>123 Street<br>Some Town</p>
code would output:
YourName
123 Street
Some Town