Hello webmaster2013,
Thank you for your question. When you first sign up an email is sent, that includes a link for creating an AMP password.
If you no longer have the email, or are having trouble logging into your AMP account, due to your password, you can click the link on the AMP Login Page, that says I don't remember my password.
After entering your Domain Name and Email address, a password reset link will be emailed to your primary address on file. You can then click the link to create a new password.
If you have any further questions, feel free to post them below.
Thank you,
-John-Paul