Pretty simple. Check out the spreadfirefox site…
http://www.spreadfirefox.com/
Notice that all the posts say ” “‘s blog. That means each person has a separate blog they can post to and that post can show up on the front page. The admin can allow anyone to sign up for an account and start posting, or blogs can be restricted to only selected bloggers. The admin can allow all posts to go to the front page, or the system can be configured to allow only selected blogs to show up. You can even elect to have no blog posts show up on the front page and instead show other types of content. You can also see all the posts by one person by clicking on the link for that blogger.
By default all the blogs use the same template, but there are modules where bloggers can actually select a preinstalled template specifically for their blog.
The system can be pretty sweet. Drupal is one of the better open source “CMS” projects. There is a pretty good learning curve to the system, especially if you are an EE user because EE makes everything so easy. If you are a developer, Drupal has an extension system much like that of EE. Unfortunately the system is much more difficult in the creation of custom templates.
The best way to figure out if Drupal is for you is to install it and give it a test run. I can’t really give you a bunch of info because I have not used it to its full potential. The system takes a bit to learn, and in the hands of a savvy programmer it could be pretty powerful.