In the module 2 of introduction Digital Devices they have discussed in detail about the operating system which is needed to run the computer. Operating system is a program which helps to co-ordinate with other programs in the computer. Computer is nothing w/o OS.
There are many types of Operating System available in the market like Windows, Linux e.t.c. All the programs need Operating system to start , but OS automatically gets started as we start our computer or laptop.
See the video to know more :