The login / password is admin / demo. It's pre-populated so just hit the login button.
Test the demo freely, there is no limitation to the number of ads or campaigns you can create there. Just don't forget this is a public demo available to everyone. Please don't enter any sensitive data in it and don't expect that noone will mess with your tests.
If there is anything unclear or you have a suggestion, feel free to contact us at firstname.lastname@example.org