Question

what are function if operating system?easy

Answer 1

An operating system has three main functions: (1) manage the computer's resources, such as the central processing unit, memory, disk drives, and printers, (2) establish a user interface, and (3) execute and provide services for applications software. 

Answer 2

Operating system is a set of program which operate your different functionality.
It create a path or a way that a user can access with their hardware, this software may or may not be Graphical User Interface (GUI) (like modern UIs or Windows 7 as an example) and it may also be Non-graphical user interface (like basics and previous version of Microsoft Windows 98).

Functions:
Δ Create a way or path that a user can access their hardware.
Δ User interface help user to perform different operations.
Δ Help a user to run different application games, browser that you're asking this question etc.
Δ If you're a developer then you can make your own OS, software with help of different IDEs.