Форуми / Cotonti / General / Make new box for menu?

I decided to make a site with 3 column, i have change the site size in CSS and in midle it's normal with the size that had previously...

I know HTML and a part of CSS but now i'm trying with this tutorial, if i can't i post here the problem which i can't fix...

Thanks a lot pieter and ez.

Added 21 days later:

Please who can help me for this...?