Within commerce you can easily take a look at a customer from an overall perspective. You can visit the list of customers from your admin CP by visiting Commerce>Customers>Customers.
When first opening this section you will see a list of all customers within your commerce system at present. You can view the details of any of these customers by selecting the icon on the right of each record.
Customer records will give you an overall view of your customers current standing within the commerce system as you can see in the image below. From here you can add invoices, create support requests on behalf of your customer, add notes and more.
On important area of this section is the management of alternative contacts. On selection of "Manage Contacts" you will be shown a list of members on your site who can also manage this customer account. These can be added to from here in the admin CP, but also can be added by the customer within their client area (discussed in another guide).
You can create a new alternative contact for the customer by selecting the "Create New" button in the top right, or edit/delete current ones using the buttons provided at the side of each record.
When adding a new alternative contact, you will be asked to add the members name (auto filled upon typing) and optionally can associate the contact with a specific product. You can then set the options you would like the alternative contact to be able to access.