The four basic functions of a computer system are as follows:
Let's look at each individually:
Transferring of information into the system. This may be through a user input device - i.e. keyboard, mouse, scanner etc.. Or though previously loaded software/program, cd etc.
Output is the exact opposite of input. Output is the function that allows a computer to display information, from the system, for the user. This can be accomplished through the monitor (or other graphical display), printer, speakers etc.
This is where the computer actually does the 'work' - manipulating and controlling data over the entire system.
Most computers are able to store data both temporarily (in order to process), but also long-term (i.e., permanently). Storage takes place on hard-drives or external storage devices.
Although on the surface it seems that computers are very sophisticated devices, capable of accomplishing complex tasks, in fact, computers can only do a limited number of very simple tasks on a hardware level. Their apparent complexity is due to their ability to do basic tasks very quickly and for programmers to create complex algorithms which break down complex tasks into the very simple steps that can be accomplished by computers.
The first basic function a computer can accomplish is storing information, typically in binary form (as either a one or a zero). Next, a computer can retrieve that information for processing.
Most computer processors can do four possible logical or Boolean operations on binary digits, NAND (not + and), OR, AND, and NOT. More complicated operations are build by combining these simple operations.
Finally, a computer can communicate information by sending and receiving electrical pulses along connectors known as buses.