A div is like a box, in terms of appearance (if you just attach a border to it) and function.
You make a div and you put stuff in it, anything at all.
It allows you to separate content up into separate areas.
If there are several bits of content that you want to stand out from everything else around them, put them in a div. An example could be a quote from someone, the quote goes in the div, and you style the div however you feel appropriate so that the div stands out.
