You can view the details of your client's order by heading to the main menu and clicking Selling » Orders.
When you first visit the order screen you will see a list of your currently open ("new" or "ordered") orders. To view previously fulfilled or canceled orders, or to simply filter the open orders by name or order number, click the box next to "Showing Data For:" and change the filter/search details. Once you've selected the filters of your choice, click Apply to view the filtered results.
To view the details of a specific order, either click on the name associated with the order or click the Options menu and select View Details.
You can add a note to the order details page that only you can see by clicking the Add Private Comments link.