If you can only post in the "Community Questions & Feedback" forum, then you need to do one of two things.
1. Open your e-mail and check to see if you have received an e-mail from PC. If you have then follow the activation link provided in the e-mail, and you should be able to post in all the forums.
2. If you didn't get the email for some reason or another (perhaps an error was made when you input your e-mail during registration) then just PM one of the Praetors or Administrators about it. They will change your usergroup for you so you will be able to post.