how can you learn english?

The basics of English are simple. There is no adjective and noun declension and conjugation is very simple. The tense system is a little complex and you will soon see that translating something into an equivalent tense in your mother tongue won't always work but it's generally easy to pick up when you see how the language is used by the native speakers. What is the most difficult for foreigners is the fact that English is extremely idiomatic. I think that's the biggest challenge for a foreigner who wants to speak English like a native.