You can use CAIRIS on any modern web browser. To start using CAIRIS, visit the site hosting CAIRIS services, e.g. https://demo.cairis.org, and authenticate using the credentials provided. For example, on https://demo.cairis.org, you can login with the username / password of test / test.
Once you login in you should see the home page, which provides a summary of threats, vulnerabilities and risks, and the threat model for different environments.
Once you have finished working with CAIRIS, click on the Logout button.