Hi Edison,
you can maintain the specific operation as external operation through PP02 control key in the routing
if it is a sub contracting means for that operation whatever material you are using that has to define as a F-30 in the material master
while converting main planned order to production order system will generate the PR for the specified external operation
you can covert that PR to PO and do the GRN then use that material for further operation while making the operational confirmation through CO11N
Regards,
Venkatesh..