An individual contact can be added via via menu option New -> Contacts or the ‘+’ button on the Contacts screen. In both cases, a popup appears where all relevant information can be placed. In the field ‘Contact type’ you are able to indicate which type of contact you would like to add. For instance a company, supplier, personal friend, prospect etc. When finished, click on the save button and your new contact will be added and you will be lead to the contact’s card.

It's also possible to add contacts from your Inbox. Click on the '?' icon before the name of an unknown recipient to add it as new contact to the database. 

Add multiple contacts through a mass import. At this moment, mass import from .CSV / .XLS file, Mac Contacts, Office 365 or Mailchimp is possible. Read here how to do a mass import.