Processing with an Individual Purchase Order 
Purpose
You can use this form of processing to assign tasks to an external company based on individual purchase orders.
These purchase orders can either be settled relative to resources, or based on a fixed price for the total expected output. They can consist of items for material or for services.
Prerequisites
You mark the operations for orders to be processed externally as operations to be processed externally using a corresponding control key. In the standard system, this control key is PM02.
You create the external company in the vendor master record, which is maintained by the accounting and purchasing departments.
Process Flow

You can also configure the use of collective purchase requisitions in Customizing under Functions and Settings for Order Types ® Define Change Docs, Collective Purc. Req. Indicator, Operation No. Interval.
Purchase Orders).

Example 1: You have agreed a direct labor hour rate of $ 80 and assume the work will take four hours to complete. In fact, five hours are required; a total cost of $ 400.
Example 2: You have agreed a fixed price of $ 10 per meter of cable laid and assume that 40 meters of cable will be used. In fact, only 35 meters are required; a total cost of $ 350.
Example 3: You have agreed a flat-rate price of $ 400 for the laying of 40 meters of cable, and assume the work will take four hours. In fact, 50 meters of cable were required and the work took five hours; a total cost of $ 400.
See also:
MM - Service