A computer is a device that inputs, manipulates, stores, and outputs digital information based on stored instructions known as programs.
The first main function of a computer is input/ output. This function is what enables the computer to communicate with external devices such as screens, printers, keyboards, the internet, or pointing devices. Without the abilities to communicate its results or stored information or to accept instructions, a computer would be useless.
The second main function a computer has is the ability to store data. This can be in either volatile or non-volatile storage using a variety of media, such as DVDs, CD ROMs, flash drives, hard drives, or even cloud storage.
Finally, a computer is able to manipulate digital data. Most computers operate on binary data, performing large numbers of very simple operations very quickly in order to perform complex tasks.