What is the rôle of the operating system in the computer

Question

Operating system

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.”

https://homepage.cs.uri.edu/faculty/wolfe/book/Readings/Reading07.htm

Answer 2

What do you mean by managing computer's resources please