The responsible/authorized person can approve a confirmed Requisition. Approval can be controlled by using Access Attributes. You can add the name of the Approver ('Approval Required From' field ) after creating a Requisition only for reference purpose. However anyone can approve if they have access / authority to approve.
In order to perform this activity, you need to have a confirmed Requisition.
As a result of ths activity, the status of the Requisition changes from 'Confirmed' to 'Approved'.