Using divs is simple, what im gonna write might not be the BEST way to use it, but its how you actually use it.
Inside your html / php ... page
CODE
<div id="somename">
Some Text
</div>
Inside your .css page
CODE
div#somename { // must be the same name as the id you set on your html / php page
margin-top:150px;
color:#FFFFFF;
width:10px;
height:10px;
someothercss:hahaha;
}
What you actualy do is set "variables" inside your style.css and you "call" the "function" inside your html/php and these "variables" will apply.
Not the words to use i guess since i did not learn off the book but by my self but it is what it is, you set a div name, you give them sizes, colors, and you just use it on your page.
Div's are not just like tables. They can be used as is (wouldnt suggest it) but it can be used for many things, first to give a name to a certain element... also to set a size, or a color to this element.. can be used for many things, i personally never see sites without div's... i always use them like i will always use <table...