Login to Zimbra admin panel, then click on the Accounts at the left hand side of the window and after that click on New.
image 1
In this section at first write the User Name and the Last Name (as shown in image 2a) as these are two mandatory fields you have to fill up, then scroll down the page and typed the password (as shown in image 2b) for mail client login. Last of all click Finish.
image 2a
image 2b
A new mail user account in Zimbra has been created.