Registering your customers will give you the ability to grant them various privileges such as discounts, loyalty program, specific communication. It will also be required if they want an invoice and registering them will make any future interaction with them faster.
Create a customer
From your session interface, use the customer button.
Create a new one by using this button.
You will be invited to fill out the customer form with their information.
Use the save button when you are done. You can then select that customer
in any future transactions.