Hey.. Decided to do something out of the ordinary today.. (This is a super long post) Hope you dont bored out. :)

Ever wonder how to build a CPU from scratch? Its kinda easy actually.. u just need a phillip head screwdriver and alot of time.. Here it goes..
This is from my Pentium 3 CPU.

This is a the cpu casing or chassis.. the aluminium box that u press the on button

This is a mama-board/motherboard/circuit board/mobo/board's mother/mother of all boards. (Should celebrate Mother's Day for it, its a mother also). It controls all the processes in the computer. The black fan is the processor located. This suppose to be in museum already.

 
The 1st step is to plug the power switch to the mobo cpu pin (located nearby)

Then make sure the mobo is fitted rightly at the output that comes with the casing. It'll fit perfectly. 

The screw it according to the hole that provided by the casing, or in some cases, u got to put the mobo stand 1st, before screwing it in. Mobo should not stick to the casing.. Coz it will create heat.

Thats your power supply unit. The one and only parts that has many wires like hair.

PSU normally situated at the top of the casing, place it and screw it in.

PSU has only one biggest head among the other heads for power connection. Plug it in to the mobo, u can see the only biggest head in the mobo.. tats the one

The casing will provide some wiring for the power switch, and some LED indicator, take note.

Plug those at the mobo, situated bottom right. the motherboard got state which position for which plug head. Put it accordingly.

Thats a RAM, the one without horns and make no noise. 'An ideal pet indeed' hahaha...

Put the RAM into the slot that provided. Normally its at the right side of the processor. Position it 90 degrees, and put it in with a little force and lock it in place.

Thats your CD ROM, the one feed it with flat doughnuts. Put it at the top bay, the widest bay that available in the casing. Screw it at the sides.

It will come with the grey coloured wire. Plug it at the back same goes with the power cable from the PSU (the coloured wires)
This step goes the same if u have more that one drives.

Plug the grey wire to the mobo For this time, its the same colour head with the mobo.

Looks familiar? Thats your hard disk drive(Computer's Stomach), the same step with the CD ROM, only place it in a smaller bay.
NOTE: the gray wire is a separate wire than the CD ROM drive.

Plug the hard disk wire at the same place, where the CD ROM grey wire located, just next to it.

This is ancient stuff, skip this if you are not using this anymore.. YES its a floppy disk drive. What's floppy disk? next time..
It is still the same step like the putting in the Hard disk, only that this need a 'out room' for it (Just like a CD ROM) normally casing will provide. 

Floppy has a smaller pin head for power, so use the smaller(smallest) pin head that the PSU provide. 
And use different grey wire, in this case, the wire are slightly smaller that the previous two, but same step and place.

In case u didnt know, this is a graphics card/video card. (Tats a Nvidia GeForce 4)

Place the Graphics Card to a slot that located slightly below the processor, the pic will guide. (This is an old AGP slot, but modern one are still at the same location). Slide it in from the side and screw it tightly. Reffer to the pic.

Thats network card, its optional, because most ppl now uses ADSL modems. Network card mostly for dial-up. Fix the card unto a white slot below the graphics card slot. Its called PCI slot (Peripheral Component Interconnect). Its the same step how u place the graphics card in. 

Thats sound card. Needless to say, same way and step with the Network Card.

And finally, screw back the side casing and  'Voila!'

A working CPU.

Thanks for the patience. But this post doesn't guarantee correct steps, its mainly the rough idea how to build a CPU/System Unit.