Customer Details Page
Going to Downloads → Customers and then clicking View on a customer brings you to that customer's details screen. Here's an example:
You may also get to this page from the admin page for a single purchase. The single purchase page lists the customer, and you may click View Customer Details.
The image comes from the WordPress user profile. In this case the user doesn't have one set, so it's using WordPress' fallback gravatar icon.
EDD Personal Information
Next to the image we see the Customer's name. Below that is their email address. Below that is how long they've been a customer.
Lastly in this section we see a User ID. This is their WordPress user id. In the top right of the Customer Details you'll see another number (#2 in the example above). That number is their EDD Customer number.
Next to the User ID is a link to Disconnect User. This disassociates the WordPress user id with this EDD user.
When there is no association between and EDD user and a WordPress user, that spot holds a link to browse WordPress users, and create that association.
To the right of the EDD Personal Information is the Customer's address. This data comes from the WordPress User Profile, so if there isn't a WordPress user associated with this EDD user there will be no address listed.
Below the Customer Information you'll see a Completed Sales section and a Lifetime Value section. When you click the Completed Sales section you go to the Payment History page with a filter in place for only that user.
Below each of those (not pictured in the example above) is a list of recent payments and a list of Purchased Downloads.
Below the customer image is a link to Edit the customer. This allows you to edit the customer data without a page reload. Example:
In the top right of the Customer Details screen is a collection of tabs. These have additional functionality which will be covered in other docs.