How could we learn english?

Go to England and/or USA for a year and you'll learn English very fast and correctly. Of course you'll need basic understanding and mastering of the English language first before you go do that. Watching TV, listening music comparing what you hear to the lyrics, doing grammar excercises are all methods you can use to get basic understanding.

you can easily learn a certain language by listening to it, and using it. watching English movies and reading books or newspapers will help a lot.