Under your account navigation you will see a link for My Groups & Organizations. That link will take you to a page that lists the groups you currently belong to.

If your group has not yet been created, click Create New Group above in the grey permissions bar. You will be asked to name and describe the group as well as answer a few questions.

Once your Group is created, you can customize it by adding new panels, text and images to the Group's profile pages. You will also have access to the group Control Center where you can manage a member roster, update group information, view group events or make purchases on behalf of the group.