Whenever a customer sends a message or opens a dispute, a store administrator will see a notification about it on the homepage of the store’s Admin area:
To access the messages themselves, click the respective link (“Messages” or “Disputes”). It will forward you to the Messages page of your store Admin area (Orders -> Messages), where you can process incoming requests from your customers:
Another way to see incoming order messages is when working with the order details. While on the order details page, you will know you have new unread messages/disputes submitted with regards to the current order if a small number label displays next to the Messages tab title. The number on the label will show the number of unread messages.
Note that you will also be notified about any new messages/disputes via email.