Items transfer to order screen below the highlighted line. If you need to change the order, cut and paste functions allow you to do this; look to the Edit menu for these options.
1. Using your mouse, drag across the item(s) to highlight them for the move.
2. Use Edit, Cut (Ctrl+X keyboard shortcut) and the items disappear (copied to temporary clipboard)
3. Highlight the line where you wan the items to appear. Use Edit, Paste (Ctrl+V keyboard shortcut) to make items re-appear in the desired location.
Note the Order screen items should now be displayed in the desired order.
This is also covered in Training Videos - How Do I? list under Order Screen: Moving/Deleting Line Item(s) on an Est/RO/Inv