Currently you can only use the Mobile App on Apple devices. We are working on offering SPITCH on Apple devices for Mobile-Web as well.
To join a community, a member of that community must invite you. To do this, a manager of the community must click on “Add”, copy the link and forward it to you. As soon as you open the link, you will find yourself in the “Community” area. Finally, confirm that you want to join the community.