If I want to learn English, what to do?

I think the best thing to do is to practice. "Practice is the best teacher."

It doesn't matter what language one is learning, the best way to do it is to immerse yourself totally in it.

Is English being taught in school in your country? From what country are you. I learn English in my primary years , because its one of our subjects in school.

they have a website that you can learn. Durolingo

Mylot interaction is one great way to improvize on English.

you have to do practice such as read English newspaper,books and try to speak in english

If you have a close friend that you always hang around with and who speaks English very well, make an agreement that you will not speak your native tongue when you are together,watch English movies and tell him or her to correct you if you make a mistake in your grammar or pronounciation.

Well I think watching English films does help a lot as well as reading English books.

Try the link I give to you here:

Read English materials,listen to English news or conversations and watch English movies

If you try writing in English, you'll encounter situations that would make you wonder whether they are grammatically correct or not. You can try looking them up in the internet so you'll know which is right or wrong. Plus, it's a lot better if you read English novels by people who speak English. It's good to learn from the people who speak the language after all.