The PO History can be accessed by selecting Purchasing and then PO History. This section of MVP One will display a list of all Closed Purchase Orders. This will include Completed, Invoiced, and Cancelled POs. 

When POs are Closed (State = Closed) or Cancelled (Status = Cancelled), they will be moved from the Purchase Order List (Purchasing> Purchase Orders) to the PO History.

For a list of actions that can be performed from the PO History, please reference this article.