How does Literature express culture?

It expresses itself through time, place and person(s), history, experiences, gender, philosophy, antiquity, heritage, religions, trades, education, dialects, love, animals, vocations, traditions and all the human foibles, etc.

The literature shows ideas, the ideas record the thougts of the autor. When we read, we increase our culture

"The man who writes about himself and his own time is the only man who writes about all people and about all time. "

George Bernard Shaw

Take that as your starting point and switch on your own brain.

No offense. ;)

Look up something on socialisation, what defines "culture" and take into consideration the various reasons why people write (in the literature as art sense, not everyday writing). There you go. Good luck with your paper.