The customers of your shop can set up a customer account during the order. When a customer orders as a guest, he can choose to register as a customer. In this case, he determines a password. He can then use these credentials during new orders, so that he does not have to enter data such as his billing and delivery address again.
In the future it will also be possible that customers can login anywhere in the shop and can for instance view old orders or edit their delivery addresses. This feature will be introduced in the coming months.
When you visit the Customers page in the Administration area, registered customers in the table are marked with this icon: