When you were in school, or when your children were, you used flashcards. Those handy little cards are useful to learn everything from spelling, addition and subtraction, to foreign languages, and mathematical theorems.
Those cards reinforce learning by zeroing in on one point, until you master it. On one side of the card, you put the question or problem you want to learn, with the answer on the flip side.
Perhaps it's a math problem, like 7 x 3. Flip it over: 7 x 3 = 21. The flashcard's simple question-answer format reinforces learning because the card is simple to flip over and over, until you memorize the answer. "7 x 3?" "21." "7 x 3?" "21."
Flashcards, or index cards, can also be extremely useful to memorize science and history facts, or to study music. You might write "Gettysburg Address" on one side, with the answer, "Abraham Lincoln, November 1863," on the other side. For music, you might write "C sharp" on one side, with that note written on a music scale on the other side.
Still, as great as flashcards are, they have limitations. Notably, they come with none of the bells and whistles that really help children, college students and business people to learn, and memorize important information.