You don’t really “join” APPL.  If you play on an APPL team there is a fee that you will pay when you register yourself on that team.  If your club or community has indicated an interest to play in APPL you should contact your club APPL administrator and indicate your interest in being on a team.  You can also form your own team.  If you have a network of similar skilled players that enjoy playing together and they are interested in joining your team, you can register a team on the APPL website.