Thread:Project:Support desk/GNU GPL

I'm building a site based on MediaWiki.

My questions are:


 * 1) Can I change the layout of the site (example: add a right column with polls)?
 * 2) It is permitted for commercial use (example: advertising on the page)?
 * 3) "The GPL requires derivative works to be licensed under the same license.". I do not understand how to apply it to my site.