I saw the film several years ago, and perhaps apples might have had some symbolic meaning (but I don't recall offhand), but "Do you like apples" is not an idiom. I'd have to watch the film again to tell you what, if anything, apples represent.
The expression is "How do you like them apples?!?" It means, idiomatically (with intentional bad grammar, to imitate a working class style of talking) "I challenge you to do something if you do not like what I have just done or told you..."
I am going to marry your sister, and I don't care whether you approve or not! How do you like them apples?
I enjoyed the movie. It's also where I learned of the singer Elliott Smith (who sang several songs in the film) who then became one of my favorites. But unfortunately, he committed suicide a little over a year ago by stabbing himself (!).