Quizster is currently available as a web app. In other words, it is available as a website accessible by visiting http://app.quizster.co or by going to http://quizster.co and clicking on the "Use App" link. In the near future, after we finalize a few more features, we'll also release downloadable versions of the app for iPhone and Android.
Teachers sign up for an account at http://app.quizster.co and create classes and assignments. When a class is created, a four digit class code is automatically generated. Students need this class code to join your class.
Students sign up for an account at http://app.quizster.co and then join a class using the four digit class code that was generated when the teacher created the class. Once a student joins a class, they will automatically see any new assignments that the teacher creates.
Please see Using Quizster - A Detailed Step-By-Step Overview for more details.