On the backend, you will see all of your customers in a single place.
You can add customers in several ways.
Allow your customers to register: Your customers can register for themselves. The registration URL is- <Your Customer Portal URL>/portal/register
Make sure you enabled the customer registration in the Client Portal Settings.
Manually Adding a Customer: You can also manually add a Customer. To add a customer click the "Add Customer" button.
Importing Customers: You can also import the customers using a CSV file if you have a large customer database.