This is the 492nd most frequent Ukrainian word.
один
"One" (the number).
Here, 'один' is used to specify the quantity of the noun 'фільм' (movie), meaning 'one'.
Я бачив один цікавий фільм.
I saw one interesting movie.
In this sentence, 'один' specifies a single person out of a group, 'one of'.
Один з моїх друзів допоміг мені.
One of my friends helped me.
Here, 'один' is part of the expression 'одне одного', meaning 'each other'.