There are a number of ways to create a contact,
bulk import during initial setup,
and when building the guest list. Every guest is checked against the contact system and created if it already does not exist.
APIs
create a contact individually.
ā
From [CONTACTS], click [Create Contact].
Enter the required information such as the Email, First & Last Names.
This is the KEY and is the unique reference to a contact
It may be important to set the Business Unit (BU) which may be used to isolate contacts across contact owners (ie. Other business Teams).
Contacts are often grouped -these can be used for filtering and searching.
Does your organization require other fields as mandatory?
TIP:
Mandatory contact fields can be set in the [Company Config] by the Client Administrator. 
From the Contact tab, add additional contact details including; Company, Job Title, Account Representative (Contact Owner), etc.
How to invite guests from my contact list?
Where do I find my guests dietary requirements?