First, make sure you have a Forum account and are logged into it.
Then, while in game with your character, type:
forumaccess
This will provide you a link to click. Once you click on the link, your in-game account will be associated with your Forum account, and you will get full posting permissions.
If you want to also access the Flames forum:
forumaccess flames
That should be it. There is no manual approval. If you use the same Forum account name as in-game, posts to the Poetry board and such will link to your name. If you use a different name, your in-game account name remains hidden to others here.