A computer system is a combination of hardware and software designed to process data and perform tasks. The hardware includes physical components like the central processing unit (CPU), memory, and storage devices, while the software consists of programs and operating systems that instruct the hardware on what to do. These systems can vary in size and complexity, from small devices like smartphones to large systems like supercomputers. They are used in various applications, including business, education, and entertainment, enabling users to perform tasks such as browsing the internet, creating documents, and playing games.