If you navigate to Rentals > "Any rental">Amenities you will find the whole list of amenities available in BookingSync :
From that on, you can go in the Website app> Amenities where you can choose you want each amenity to be searchable and/or visible.
searchable amenities are displayed as criteria in the search bar of the search page.
visible amenities are displayed in the amenity section of each rental page, no matter if they are checked in BookingSync for this rental or not. Then, the amenities checked for the rental appear in your primary colour whereas the non-checked amenities appear in light grey.