There is no evidence that Benjamin Franklin said it. Quote Investigator traces the idea to the Chinese philosopher Xunzi, of the third century BC, whose ranking runs from hearing, to seeing, to knowing, to doing. In English it circulated for decades as a “Chinese proverb”; the credit to Franklin appears by the 1980s.
What it means
People learn least from being told, more from being shown, and most from doing it themselves. It is a short case for learning by practice rather than by lecture.
Where it comes from
The passage in Xunzi (chapter 8, “The Achievements of the Ru”) reads, in Eric L. Hutton's translation as quoted by Quote Investigator: “Not having heard of it is not as good as having heard of it. Having heard of it is not as good as having seen it. Having seen it is not as good as knowing it. Knowing it is not as good as putting it into practice.” It was in English by 1928, in Homer H. Dubs's translation.
Shorter versions spread in the 1950s and 1960s as a Chinese saying, for example “If I hear it, I forget. If I see it, I remember. If I do it, I know” (1955), and “Tell me, I forget; show me, I remember; involve me, I understand” (1974). In 1986 a book on language teaching gave the three-part version as “the words of Benjamin Franklin”, which is the earliest Franklin credit Quote Investigator found.