To learn is to acquire knowledge or skill by study, instruction, or experience — and, in a lighter everyday sense, simply to come to know a fact.
The two senses differ in what they cost. Learning to sail describes a durable change in capability built over time; learning that the flight was cancelled describes the arrival of a single piece of information. A third sense, now mostly theatrical, means to commit to memory: an actor learns a part. English keeps all three under one verb, which is why the word slides so easily between the profound and the trivial.
The origin sharpens the first sense. Learn descends from Old English leornian, through Proto-Germanic, from a Proto-Indo-European root meaning "track, furrow, trail" — the same image that gives last in the sense of a shoemaker's form. The underlying figure is not receiving a deposit but following a track: knowledge as something walked into rather than handed over.
For several centuries learn also carried the causative sense — to teach. It was ordinary usage in Early Modern English and appears in Shakespeare, then fell out of favor with eighteenth-century usage guides and is now firmly nonstandard, surviving in dialect and in the mock-threat "that'll learn you." The loss left English with a clean division of labor: 📝teach moves knowledge outward, learn takes it in, and no single verb covers both directions any longer.
"Experience is a good teacher, but she sends in terrific bills" ~ Minna Antrim, 1902
"To spend too much time in studies is sloth." Sir Francis Bacon, 1597-1625