Last Updated: Dec 28, 2018 10:10AM CET
You can access the address book of your webmail interface:
The username is the complete email address, for example: firstname.lastname@example.org.
The password is the one you created when you activated this mailbox.
Click on "Sign in".
Click on "Address Book" on the top left.
New contacts can be added if you click on "Contacts" and click on New, then on Add contact: