A supermarket is a store with many different goods. Above all, you can find goods there that you need daily or frequently. These are mainly food, but also things to wash or keep the apartment clean.
Even in the past, there were stores for such things. They were called general stores or corner stores. But a supermarket is much bigger. Besides, you don't ask a salesman there to give you the goods. You walk through the supermarket and take the things you want to buy. This is called self-service. It's been around since about 1950.
At the checkout, a clerk used to have to type in each price individually. Then came more modern cash registers that can scan a bar code. It's much faster for clerks. Today, more and more supermarkets even offer checkouts where customers can scan their goods themselves. You should be honest about this, but there are also controls.
Supermarkets are usually not individual stores. A supermarket belongs to a chain of many stores of the same brand, like Edeka, Aldi or Walmart. It is difficult to say from when such stores started to exist. In Germany, the idea caught on around 1960. In Switzerland, only a little later.