How do I use other user mailboxes?

How do I use other user mailboxes?

I can use my main user but I can't use the others user I made. For example, If I have 2 users, my main one called admin@domain and the other contact@domain. How do I access contact@domain when every time I sign in it goes straight to the admin mailbox?

Thanks, I just signed up to Zoho so I'm still getting use the interface. I like it.