The Layer Underneath Everything
Every computer and phone is doing two things at once. There is the bare hardware — the processor, memory, storage, screen — and there are the apps and programs the user actually sees. The operating system is the layer of software that sits in between. It manages all the underlying hardware, and it gives every other program an organized place to run on top of it. Without an operating system, an app would have no idea how to read a file, draw on the screen, or talk to the network.
What the OS Actually Does
The operating system handles a long list of jobs quietly in the background. It decides which program gets a turn on the processor, and for how long. It tracks where files are stored and lets apps read and write them. It manages memory, juggling many programs at once so they do not collide. It controls input from the keyboard and touchscreen, and output to the display and speakers. It also handles the connections to networks, cameras, microphones, and printers.
The Face You See
The operating system is also the part of the device the user most directly interacts with. The home screen of a phone, the desktop and Start menu of a computer, the way windows open and shut, the way you copy a file — all of that is the operating system, not the apps. When you switch between apps, you are using a feature of the operating system that lets them share the same screen.
Familiar Names
Different families of operating systems run different kinds of devices. Windows runs on most PCs, macOS runs on Apple computers, and Linux is widely used for servers and many other systems. On phones, Android runs the majority of devices, and iOS runs iPhones and iPads. They look very different on the outside, but each one is doing the same fundamental job — managing the hardware so the apps you actually care about can simply run.
Source
This article was written using information from Wikipedia.