width content

I’am new to wordpress and trying to integrade wordpres in my site. I load the index.php in a existing table (by the include(); php function).

I just want to have limited blog functions so I removed most of the header, footer and sidebar. But now the width of the content in my table is aprox. 60%. id like to be 90% but I cant seem to find the setting. I’d think its in the style.CSS file. where and how do I change the width of the content.

Is there a explanation file of different CSS classes?