To request a roommate, simply tap 'Request as Roommate' on their profile page. You can view any user's profile by tapping their card.
Include a message with your roommate request. After the request has been sent, you can see the request in the My Room tab of RoomSync as on 'Outgoing Request'. As soon as the user confirms the request, you'll be notified and the user will appear under 'Roommates' in the My Room tab.