In order to join a crew, you’ll have to request access. You can do so by tapping on the crew icon of a member of the crew you want to join; this is the icon on the left of the “Message” icon when you’re viewing someone’s profile page. At the end of the crew description, you'll see the "Request Invite" button, which will alert the crew's admins of your interest.

After you've been approved, you'll be able to view all your crewmates' activity and access crew rooms by tapping on the (fancy newly acquired!!) Crew Icon next to "Edit Avatar" on your profile page.

Be sure that you aren’t already a part of a crew, or have left your current crew, before requesting to join a new team! You can only be a member of one crew at a time, and no one can add you to their crew if you already belong to another.