A Networking switch is a device used to extend networking connections to other devices. Practically speaking for the average person, it’s best to think about them like power outlet strips.
You plug your switch into a source of internet, and then anything you plug into the switch’s ports can share that source of internet, pretty much just like a power strip. The analogy even holds when I say that the one source connection is being shared by all the plugged in devices.
A switch is great to get more ports, or extend network coverage into a “remote” area like a different floor. Office buildings are often built with networking closets on every floor. Recently Power over Ethernet has made it a popular choice for all sorts of use cases, like phones, cameras, and even lighting panels, increasing the demand for ports, and therefore switches to service them.