You have the possibility to add new customers via the shop backend.
Log in to your shop backend and go to the menu item "Customer > Customers". Click on the "+Create" button to get to the the interface for the relevant customer information.
All required fields are marked with a red *.
After you have entered the necessary data, click on the button "save" to create the user finally.
Important: The customer doesn't have an account at this moment! Under the following link you will find instruction how to send an account invitation to the customer: Sending account invitation