An operating system (OS) is a collection of programs that controls the overall operation of the computer system. The operating system controls and co-ordinates the use of the hardware among the various application programs for the various users. So, it acts as an interface between the user and the compurter hardware. 
The functions of operating system are listed below:

1.  The scheduling and loading of the program in order to provide a continuous sequence of processing.
2.  It controls hardware resources e.g. Input, output or storage.
3.  It protects hardware, software, and data from improper use. 
4.  It manages the use of the main memory.
5. It checks equipment malfunctions and displays error messages.
6.  It manages files stored on the disks.