It sounds like what you want is a bulletin board system and not WordPress.
You have a one-click install of the phpBB3 software (the same that is running this board). The phpBB software is very customizable.
Another option is to use the bbPress plug-in to WordPress, assuming that you want WordPress. I do not know anything about bbPress other than it is well recommended for WordPress installations that want to do what you wish.
If you still wish to allow people to register and then post articles, you need to set the level for the new subscriber from "subscriber" to "author" or higher. Being an "author" will allow the person to post their article but not change another article. To do that the person needs to be an "editor" level. The level for new members is located in the settings/general tab.
If I wanted to have a board, I would not extend Wordpress but use a "real" BB system such as phpBB3.