Are you saying
1) that
www.domain.com takes you to a set of web pages and
www.domain.com/blog takes you to your wordpress site? or
2) even though wordpress is installed in
www.domain.com/blog you want
www.donaim.com to get you there?
In case (2) go to the Wordpress.org site and there is an explaination on how to do that.
In case (1) where you want to add a page link to something outside the wordpress site, do a forum search, 'Adding a item to the page menubar for a link outside the site' has been answered before.