Navision allow you to create Vendors, Customers, and Bank Accounts from contact and vice versa.
1) Go to Sales & Marketing --> Marketing --> Contacts
2) Click on Functions --> Create AS --> Customer / Vendor / Bank.
3) Click on the OK button to confirm the creation.
You can only create customer from contacts that are not associated to any customer yet. If the contact has been associated to a customer, Navision will throw an error message.