Your customer list shows the customers you've chosen to save. You can use these to invoice customers or download the list in a .csv format for import to an e-mail client. Make sure you're logged into yoru profile in Backoffice.
Open the menu Customers -> Customers.
The screen above will be shown. Click Create Customer to make a new customer in the registry, alternatively Table Mode to enter several customers simultaneously.
Fill in all the information for the customer you want to create. Finish by clicking Create at the bottom of the page.
When you take payment in the cash register you can connect the purchase to one of your customers.