If your work plan is Project Management-controlled, you will create the work plan in Project Management and occasionally open it in Microsoft Project. See Opening a Project Management Work Plan from Microsoft Project for more detailed information.
If your work plan is Microsoft Project-controlled, you will create the work plan in Microsoft Project and occasionally open it in Project Management. Mapping of resource information between applications occurs automatically when sending a Microsoft Profile file to Project Management, but you can make manual adjustments during the process. See Sending a Microsoft Project Work Plan to Project Management for more detailed information.
If control is shared, you will manage the work plan in Microsoft Project and collect actuals using Project Management. See and Retrieving Actuals from Project Management (Shared Control Mode) for more detailed information.