Despite the variety of computer types, models, and technologies, all are made up of four primary components: input devices or connections, a central processing unit or processor, storage devices, and output devices or connections. The following diagram illustrates the relationships between these components. 

If you were to compare this to the typical human, the input would be the 5 senses, the output would mostly be muscle contractions, the storage is a person's memory, and the CPU is the brain. The "program" that runs on the brain CPU might be called your mind, your personality, or even your soul.

Input devices provide data from the outside world to the processor: keyboards, mice, joysticks, microphones, digital cameras, scanners, and so forth, including various sensors for embedded computers that measure temperature, speed, throttle position, or whatever.

Output devices allow the processor to communicate the results of its work to the outside world: monitors, printers, speakers, LED and LCD displays, and all sorts of different servos and actuators for embedded computers that change valve positions, angle rudders, pump the brakes--the list is endless.

Storage devices are used by the processor to temporarily or permanently store data so that it can be retrieved at a later time. "Volatile" storage loses its contents when the computer power is turned off (the human analogy would be your own memories). The most common example of this type of storage is Random Access Memory, or RAM, or just "memory". "Persistent", or "non-volatile", storage does not lose its contents when the power is turned off: hard disks, floppy disks, CD-ROMs, DVDs, and so forth (the human analogy would be books, cave drawings, and oral histories passed from generation to generation).

The Central Processing Unit, or just "processor" for short, is the engine or brain of a computer. The processor executes a series of instructions that gather data from the input devices, occasionally store intermediate results using the storage devices, and then produce final results suitable for the output devices.

The diagram above also shows a network of some sort (perhaps the Internet, or maybe a cell phone network). The computer's interface with a network involves both input and output devices, although these may be physically incorporated into a single piece of hardware (e.g. a network interface card, or NIC). This is because the computer both sends messages out to a destination computer somewhere on the network, and also listens for messages that arrive as input to the computer.

All of the arrows on the diagram are typically realized by cables of some sort, or they may be wireless (radio or infrared) signals, or they may be "wires" built in to the computer's main circuit board (sets of these wires, or "traces", are often called "busses"). There are many, many types of these cables, each with its own type of connector: coaxial, serial, parallel, USB, FireWire, ribbon, twisted-pair, Ethernet, and so on.