You will need to establish an account in order to read your secure message. Your username is your email address.  If you have multiple email addresses you will need to use the address that the notification was sent to.

To establish a new account:

From the secure message login page, select the “First time users ‘Click here’” link to create your account. The Registration Screen that follows requires you type your email address and your new password twice, along with a password reminder phrase. Click the Submit Password button. A password confirmation email is sent to the email address you provided. You can activate the pending password by clicking the activation link in the message.

If you receive an error while trying to establish your new account, please refer to this article:

I tried to create a new support account, but it says one already exists. What do I do?