This is the 160th most frequent Finnish word.
josta
"Josta" means "from which" or "of which" in English.
Here, 'josta' functions as a relative pronoun introducing a clause that states the origin or source related to 'kaupunki' (city).
Se on kaupunki, josta hän on kotoisin.
It's the city from which he is from.
In this case, 'josta' is a relative pronoun referring to 'elokuva' (movie) and connoting the idea of liking or preference.
Elokuva, josta pidät, on todella hyvä.
The movie that you like is really good.
Here, 'josta' refers to 'kirjan' (book) and introduces a clause expressing discussion or mention about the book.