While logged into your MailChimp account, follow these directions:
Click on your name in the top right corner
Click on “Account” in the dropdown
Click “Settings” then “Users”
Click the “Invite a User” button
Fill in the email address of the user (ie., firstname.lastname@example.org)
Select the permissions level. For in-depth MailChimp assistance, select the “Admin”.
Click “Send Invite” button
MailChimp will send an email invitation to the user you added. That user will then be able to login to your account using their own ID and password (keeps your account secure). You will retain the ability to remove the user from your account.