In the 1920's, when the stock market crashed, people think about the Great Depression. However, the stock market crash alone was not the cause of the Great Depression.
When people began to withdraw a lot of money from the bank, banks weren't able to keep up paying off the loans causing banks to go out of business.
As the stock market crashed, spending on goods and services were all declined. Therefor, it made people not able to work.
Another cause for the Great Depression is when people began to produce more cars, buildings, jewelries, and many other goods. There were so much overproduction of goods that people weren't able to buy as much as they wanted.
Later on, the Great Depression finally ended when President Franklin D. Roosevelt declared a national bank holiday. It is where all banks are closed including the Federal Reserve banks.