Go there to "Groups" and request the membership of those groups your belong to. The according manager will receive a notification and only after he/she approves your request, your membership will be active and you will have access to the according sections of the forum.
Go on "Edit Profile".
Upload a new Avatar picture of you.
Go through the other sub-menus and adjust your settings.
Especially adjust your notifications. More informations how to do it are here.
Go through the "How to use this Forum" section and get to know the most important functionalities of this forum.