I "learned by doing."
I talked to my parents, other children. I watched television programs intended for children.
I also sat with my parents when they were watching television intended for adults--the evening news, for example--and heard professional announcers and actors speaking English.
I learned to read simple books by the time I was six. I loved to read and started to read books for pleasure on my own.
By the time I was nine or ten I was reading books with titles like "Half Magic," by Edward Eager; "Miss Pickerel Goes to Mars;" books by Dr. Seuss (BEFORE his "beginner books," I mean "If I Ran the Zoo" and "Thidwick, the Big-Hearted Moose"). Some of the "Rick Brant Electronic Adventures."
Starting at around age 13 or so, my school classes began to introduce formal teaching about grammar, and we started reading "classics" (Shakespeare, Charles Dickens); "subject, predicate, object." Diagramming sentences. Formally learning irregular verbs ("I think, you think, he she or it thinks, we think, you think, they think"; "Swim, swam, swimming, swum.")
But by that time I would say I HAD ALREADY "LEARNED ENGLISH."
School was merely the bridge between "English" and "educated English" or "formal English" or "standard written English."