After raising a New Purchase Order the Quantity on Order stock level will be updated. 

This is visible from the report at Reports > Material > Stock Level > Quantity in Stock.



It is also possible to view and edit this in the Edit Material page.  To do this, from the Main Menu select Set Up > Material and click on Edit next to the Material you wish to see.

You should see a page similar to

 


In the above example the Quantity on Order (highlighted above) displays the quantity that has been ordered (through a Purchase Order) but not yet received.