Explain posting of costs to 'Cost Centres'. | SAP-FICO

When you create accounting transitions in Fl / FI-AA / MM, you typically post to one or more GL accounts. While doing so, provided you have already configured in such a way, you also require the user to input the cost centre for that transactions, so that when the transaction is posted the values costs flow not only to the GL but also to CO to the appropriate cost centre.   The system will be creating two posting documents: one for FI and another for CO.
Besides, you will also be able to post non-financial information like direct labour hours from HR or SAP modules to cost centres in CO.