I added a new 10-user trial tonight for Atlassian Cloud with Confluence only. After reserving the site name, the site was created and an email was received that the site was ready to go. There was no opportunity to establish the Admin password. I searched for default Confluence password but was not successful in finding one that is expected on new Atlassian Cloud sites.

It wasn't immediately obvious that I had to use the change-password option (with the account name of 'admin') to establish the admin password. If there was a default admin password, it wasn't presented to me during setup. (Or perhaps I missed it?)