When you multiply two numbers, you increase the first by the same number that's specified by the second. In other words, when you multiply two by three, you add together three twos.
When you're doing simple math problems, you can multiply by memorizing lists of times tables — or you can add one number as many times as the second number: four times two is the same as two fours, or eight. Another way to multiply is simply to increase or expand greatly: "If the diner starts serving homemade pie, their profits will multiply." The Latin root is multiplicare, "to increase," from multiplex, "having many folds."