As a user of Tandem, you have to specify your interests and what type of person you're interested in talking to. Once you've responded to these questions, the app will suggest a number of users for you to talk to. This way, you can make sure you only have to talk to people you might be interested in talking with.
Tandem's job is 'finished' once you've found other users that match your interests. From that moment on, it all depends on you. You can start talking with them like you would from any other instant messaging app. You can even send audio files and pictures.
Tandem is a great app for learning languages, as it lets you learn the best way possible: by having real conversations with other users who are interested in the same things you are.
Requires Android 4.1 or higher