From Sketchucation's FAQs:

@unknownuser said:

You can view all usergroups via the “Usergroups” link within your User Control Panel. If you would like to join one, proceed by clicking the appropriate button. Not all groups have open access, however. Some may require approval to join, some may be closed and some may even have hidden memberships. If the group is open, you can join it by clicking the appropriate button. If a group requires approval to join you may request to join by clicking the appropriate button. The user group leader will need to approve your request and may ask why you want to join the group. Please do not harass a group leader if they reject your request; they will have their reasons.