Admin or any staff with permissions can create a new customer. A customer can be an individual person with only primary contact details, or a company, which can have multiple contacts with a single primary contact.
Primary contact is one who gets emails and other notification related to the customer deals with the company.
Primary contact can be switched easily, but the username and password required to login the customer will stay same while changing the primary contact. Although it can be updated easily.
Here, in the customer's section, you will see the list of all the customers. Customer's details can be updated with ease and if you want to add new contact details, notes, proposal, invoice, estimate, task, media file, or reminder, it can be added or managed here.