Each user account has associated with it two roles, one for the WordPress (WP) system and one for the forums. Your assigned role determines what you can and cannot do on the site. This page describes the roles most users will encounter.
Initially, users will be given a WP role of Contributor. This allows you to view information and to contribute posts. Your first post will be submitted for moderation as a check against someone sneaking in to abuse the system or a user misunderstanding the purpose of posts. Once you have successfully contributed a post your role can be raised to Author, which allows you to post without moderation.
Another WP role is Editor, which allows that user to edit other user’s posts and the front pages. Editors may be appointed to assist with the work of running the site. The Administrator is allowed to do anything.
The forum roles are separate. Most users will have a forum roll of Participant, which allows them to participate in the forums. The first topic or comment you raise will be moderated, for the same reasons discussed above. A Moderator can create, moderate or edit a forum. A Keymaster can edit forums created by other users.
There are other roles, not described here, which might be assigned should the need arise.