We explained the difference between the a visit and a property in this article: http://help.wavehousecleaning.com/en/articles/3643425-what-s-the-difference-between-a-property-and-a-visit
Now that you understand the difference here is how you can manage the extras for a property or a visit:
Property: Go to the property page > select your property> click on the edit icon
Then you will be able to manage your extras for this property:
Visit: Go to the Calendar/Visits page > select the visit you would like to manage > click on the edit icon
Now you can manage your extras for that specific visit.