To join a Squad on BTWB, you must be invited. You will be sent a link from the creator of the squad, from this link, just follow the simple steps.
Once you have opened the link, you will be prompted to Sign into your account OR create a BTWB account (for new users only).
Select to join your Squad.
If you have not already dowloaded the app, make sure you do that on the following page. The Squad feature is currently only available on your BTWB app.