The email address and password are the same for the app and the website.
Be sure you are logged out at PianoTrax.com. Then go to "log in" in the upper right corner of the website and click on it, below the space where you enter your email address and password it says "forgot your password?". If you click it, the website will send you an email with details about how to reset your password.
Once you have reset the password on the website, you can use the same email address and password to log into the app.