I installed mediawiki and Special:Version shows that ConfirmEdit extension is installed, but when I try to go to index.php?title=Extension:ConfirmEdit to configure it, I get nothing, how to go to that page to change its settings?
That's not how extension configuration works. See www.mediawiki.org/wiki/Extension:ConfirmEdit for instructions. Basically you have to edit the file LocalSettings.php in the root of your MediaWiki installation.