can WordPress do this…?

Hi, I think that this is the script I want but I am not very good with scripts so I’m not 100% certain. What I am hoping to do is have a message board / community where everyone can post (much like the communities on livejournal) and also have each person able to have their own blog. It needs to have the ability for users to sign up automatically themselves without me having to set up each account. From what I’ve read about wordpress I think it will do this but I was not totally sure what “categories” and “subcategories” meant…I think those would be equivalent to the messageboard/community that I want, is this right?
Thank you for your help!