In this section you will be able to create your pre defined extras that can be added in the reservation page.
Filling in the box for "Add a new Extra", you will be able in "level" to select if it is a per person/room/una tantum charge. Once saved they will move on the right hand side, you can still edit them by clicking on the pencil icon.
Extras price can still be customize during the assignement of the extra in the reservation page. So this extra pre-definition here is not limiting your actions.