In simple words the operating system serves as a bridge between the computer's hardware and the end user, essentially offering a Graphical User Interface $($GUI$).$ It assumes the critical responsibilities of hardware management, security provision, memory and input$/$output $($IO$)$ handling, as well as the administration of peripheral devices and processor management.

The key things in OS are:

Hardware interface: The OS acts as an intermediary between the computer's hardware and the user,

User Interface $($UI$)$: Many OSes offer graphical user interfaces $($GUIs$).$

Security: Operating systems are responsible for enforcing security policies.

Memory Management: he OS allocates and manages system memory to ensure that applications and data are stored and retrieved efficiently.