At the minute this capability isn't built into dotnetnuke (though some people use roles to give a semblance of this i.e. create an 'editors' role and let them edit pages, and then have an 'approval' role, who is able to then make the page\module visible to the other users. True content management, versioning and workflow are all items being discussed for the roadmap so will be built in at some point, but in the meantime you may want to look at some of the commercial solutions for content management & see if any suit your needs. Theres also a free option here that's worth looking at.

Cathal