How do I access my custom email address added as users

How do I access my custom email address added as users

So as a free zoho user I added mycustomdomain.com and I added users we@mycustomdomain.com and support@mycustomdomain.com from the mail admin console.

How do I access these users account to see incoming emails and also send emails.
Or how do I login to these accounts, when I try to login with we@mycustomdomain.com I get this message "This account cannot be found. Please use a different account or sign up for a new account."
I thought those accounts were created already when I create the users.

Does it mean I will have to change my account's primary email all the time?

I also try to add the account using POP3 in the mail settings, but I got a "service unavailable" error.

I don't really understand this Zoho, things are just too hard to figure out.

Please help me.