Some were just born in the US and eventually learn because there are people around them that speak English and school helps a lot too. For others they either watch a lot of English tv shows and make friends that speak English, and eventually they start learning little by little.
I say this because my mother tongue language is Spanish and I learned English by going to school and it was a lot of pressure since my family doesn’t speak English and no one around me did, but after 2 years I improved and now I’m very fluent that I even use slang.
I HOPE THIS HELPS. Sorry everything was in English
@Park_Seoyeon thank you very much! I'm a learner from China, and i have learn English for about ten years, just learn in school and when i do my housework, but i can't even get it when someone say a simple sentence and i always take a long time to speak out a sentence which I'm not sure about its correctness, and now the same.
And i think i have a big trouble, that is, when i'm hearing, i always try to write words in my brain, and it also appear when i speak. i think i should listen more and speak more. And my learning resources is too formal and short of daily conversation. and now i encounter the Hinative. hhhh i get the charm of language gradually. i love English, love Spanish, French and Japanese.omg..