assign a custom concurrent program to ship confirm document set

I am a developer and asked to develop a new concurrent program ( CP ) and assign this new CP into ship confirm document set.   Create a new CP is not an issue.  attach the new CP into ship confirm document set is not an issue too ( Order Management responsibility > shippings > setting > document sets ).  But what I don't understand is... how the delivery id or order number pass from ship confirm ( user click ship confirm then trigger to run all CP assigned to the document set ).   So the new CP know what delivery_id or order_number is shipped confirm?