Once you’ve added user authentication, you’ll have access to the User List menu. Here you can manage all your users.
Offering a chat service in your app is a way to bring users closer together, for a social app, but also to create a space to exchange, debate or even improve the internal service of a company, by allowing employees to contact each other for example.
The User Groups add-on can be very powerful especially if you plan to restrict parts of your content. It gives you the ability to categorize user groups and restrict sections of your app according to user groups (one or more for each section).