The first page under the "Customers" menu gives you a list of all the registered users on your shop.
This gives you a bird's eye view of your customers, with some details thrown in which you can use to sort and search accounts:
Title. Customers can indicate their title, which can help you better customize your customers' experience. There are three default titles: Mr., Mrs., and Miss, but you can create more in the "Titles" page under the "Customers" menu.
Enabled. Indicates whether the account is active or not. You can disable an account by clicking on the green check mark.
Newsletter. Indicates whether the customer is subscribed to your shop's newsletter or not. You can unsubscribe from it by clicking on the green check mark.
Partner offers. Indicates whether the customer has agreed to receive emails from your partners or not. You can unsubscribe from it by clicking on the green check mark. Do not subscribe a user to these emails without their consent, as this is considered spam.
Registration date and last visit can always be useful when sorting accounts.
Actions. You can edit the user's account, simply view it in full (with its messages, orders, addresses, vouchers, etc.), or permanently delete it.
When installed for the first time with sample data, PrestaShop has a default user, named John Doe.
You can use this user to test some of your shop's features, and generally browse your shop and see it the way a regular user would.
To log in to your shop using this account, use these credentials:
Email address: firstname.lastname@example.org
Before you open your shop to the public, make sure to delete this default user, or at least change its credentials! If not, malicious visitors could use it to make fake purchases, or worse.
Below the customers list is the "Set required fields for this section" button. It opens a form where you can indicate if a database field is necessary or not by checking the appropriate boxes: this way, you can make it so fields such as "newsletter" or "partner offers" are mandatory when a visitor is creating a customer account on your shop.
You can export a list of your clients by clicking on the "Export" button at the top.