In this article, we only add an individual contact, but you can import many at the same time if you want.
Learn more in Import multiple contacts.
Add a contact
Go to Audience > Contacts.
Expand the NEW CONTACT drop-down menu at the top of the page and select Add contact.
Enter the contact’s Email address or Mobile number (or both).
Select ADD CONTACT.
For mobile numbers, use either the international phone number starting with (+): +44 7000 000000; or select the country flag and enter the local phone number: 07000 000000.
The contact is now added to your account.