Try not to waste space with extra words.
Before: "There is no doubt that movie is one of the most powerful media means in the history of mankind. In the modern society, movies are popular and also becoming a part of our lives. There are several main reasons explaining for the popularity of movies."
After: "Movies are a powerful and popular media because . . ."
And now you have room to actually summarize your reasons.
Other than that, you have the basic structure down.
For example, when a person watch a western movies, he or she can have chance to know about histories, lifestyles, and so on of western countries,
This is frankly a frightening thought, that one might actually think Hollywood movies reflect anything accurately, but it will do for this sort of essay.
Your grammar isn't bad enough to obscure your meaning, though it could use polishing. There are contributors who like fixing that sort of thing, though, so I'll leave you in their capable hands for that.