To join a group, go to account admin>group membership. It looks like this.

Select your group from the drop down menu and click join group.

Once your request to join a group is approved by the group’s administrator, your group membership status will update from awaiting approval to approved

 Depending upon the permissions granted by the group’s administrator to accounts linked to their group, the look and feel of your user interface and the active version of a snippet within your Report Content Manager may change on joining a group.