This is the 17979th most frequent Polish word.
śmietanę
"Śmietanę" means "cream" in English.
In this sentence, 'śmietanę' is a direct object in the accusative case, indicating the substance being added to the soup.
Dodam śmietanę do zupy, żeby była bardziej kremowa.
I will add sour cream to the soup to make it creamier.
Here, 'śmietanę' is used in the accusative case, denoting the desired item for dessert.
Czy masz śmietanę na deser?
Do you have sour cream for dessert?
In this case, 'śmietanę' is again an accusative case form, referring to the item purchased.