Can't find out my webmail logins

Hello, I just created an account here, I was a bit excited when I found out that there are hosts providing free and unlimited hosting :).

I was wondering, what are the username and password I need to login to the webmail, I add some addresses for the site(s) I have in my account (one address for each, the usual “info@[domain].[etc]” and I set a password for each. However, when I try to login to roundcube I can’t, I have tried using the whole email address as username, I have tried using my infinity username, but I can’t seem t be able to login.

I would also like to ask about the nameservers, when I am about to add a new domain in my account, the nameservers that it suggests are these:
On the email I got when I registered here, there were these nameservers as well:

thank you