See How Do I Join My Gym for more info.
Sign into www.btwb.com, then select the "Explore" tab at the top of the page. Select "Gyms" from the drop-down menu that appears. You will then be able to search by the gym name or the location of your gym. You will not be able to join your gym from this page. For step by step instructions on how to join your gym, go to the FAQ article How do I join my gym?