Click on the blue link Add-Ons under the Rate Information folio section; if you want to add a POS, then click on the blue link POS Items right below it:
Choose the available options from the drop down menu Charge:
The configured price for the chosen extra item will appear in the Amount box; you will be given the option to amend that price by either writing a new value in this box, or by clicking on the arrows on the left side:
Insert the quantity of items you wish to add to the folio, by placing the correct numeric value in the Qty box:
When finished, click on the green button Add Charge:
The charge and all applicable taxes will be listed in the panel:
Note that all charges will appear to be Pending until you save the folio: once you save the folio, charges will appear as posted:
You will see the amount for each added extra items next to the relevant tag, under Rate Information section on the folio: