Hi,
There are two types of subcontracting for operations in a PO.
1- Subcontracting w/o material movements: It's when you only subcontract tha activity, for example, of an assembly. It's like if the vendor comes to your plant and do the subcontracting on it.
You need to créate an standar info record for material group, it means, that at the selection screen you only inform of the vendor, the purchasing organization and the plant. Furthermore, you need to change the control key at the routing (PP02, YBP2, etc.) and inform the info record and the purchansing organization (also the cost element).
When the PO is created, the system, automatically generates the purchase requisition for the vendor. Once the purchase flow is completed, when you do the Goods receipt for the purchase order, the system only do a cost input for the activity to the PO, not any godos movement. The good receipt (101) for the parent will be done at the PO confirmation.
2- Subcontracting with material movements: in this case, you transfer the components to the vendor house, he, for example, assembly them and returns the parent to you.
For that flow, you must to créate a subcontracting info record for material group. As in the previos case, you don't have to inform the material, only the vendor, purchasing group and plan and the subcontracting info category instead. When you change the control key at the routing, in addition to the fields informed in the previous case, you have to click the subcontracting indicator.
When you créate the PO the system generates a purchasing requisition type L. Then, you have transfer the components with the TR MIGO with a movement type 541 to the vendor. Once the purchase flow is done, when you do the Goods receipt, the system, automatically do a cost input for the activity to the PO and the consumption of the components. In this case, be sure that you don't have to be informed the Production storage location because the consumption is done in the Goods receipt not in the confirmation for operation.
Hope i help you.
Regards.