After Huey, Dewey and Louie come to the Bin asking Scrooge for advice on how to best use the money they have saved up in their piggy bank, Scrooge responds with a full-on crash course in economics — starting with the history of money itself, and moving on to concepts such as inflation. The master words of his little exposé (which is not unironic given the nature of Scrooge's Bin) is that "money must circulate".
Behind the scenes
This short was released in 1967. It was 'adapted' into a comic story as Uncle Scrooge and Money the very same year.
It is considered the first true appearance of Scrooge in animation, barring his pseudo-appearance in The Spirit of '43 and a cameo in the opening credits for the Mickey Mouse Club TV show (which may be why the animators, unfamiliar with Scrooge, altered his design to significantly resemble Ludwig von Drake). It also foreshadows DuckTales in that it solely features Scrooge and Huey, Dewey and Louie, with not even a mention of Donald Duck.