how to create and use <div> container ?

Hi everyone !

I've installed FCKeditor to update my website, and it works fine.
But I would like to use <div> tags instead of <table> to make up my text into pages.

There's now a "<div> container" icon on the editor, great... but how can I use it ? Where can I define the styles (in the "General" item) ? What about the "advanced" items ?
I didn't find any topic about it...

Anyone could help ? Thx in advance