The app's new home page will have Gatherings galore! When you RSVP to a Gathering from the Home Page, you will automatically be joined to that Group!
You can also join a Group from the Groups tab:
When you’re in the app, click on the Groups tab in the bottom menu. You’ll come to a screen that includes all the Groups in your building (as well as an option to suggest a new Group - here’s how to start one!). Click on the Group you’d like to join and you’ll see a description of the Group as well as members’ first names and Gatherings. Simply click the “JOIN THIS GROUP” button at the bottom of the screen and you’re in!