You don't need anything except a computer for this tutorial. Enjoy :)
Step 1: The Motherboard
There are several sizes of motherboard. The two commonly used in desktop pcs are ATX and MicroATX. MicroATX is compatible with ATX, but not vice versa.
The CPU creates another variation in mobos (short for motherboard). All manufacturers of CPU use several standards of sockets each. None of these standards are compatible with motherboards not designed for that CPU.
Motherboards have PCI slots usually, which allow for expansions such as graphic cards, network cards and firewire cards. My computer, and many others have 4 of these slots.
Step 2: CPU and Cooling
Above your CPU is a cooling fan. As the hottest component in your system, the CPU has two defenses to protect it from overheating. Firstly, there is a paste on top of your processor called the thermal compound. This is also referred to as thermal putty and thermal paste. It's job is to dissipate heat before the fan creates hot air with the heat.
On top of your thermal paste, there is a cooling fan which basically blows away the heat as hot air. Not much to explain there...
Your computer may have more fans, aside from the CPU. All will have one in the PSU, and many have fans around the system. These are case fans, which just help cool all the components and take any lingering hot air from the CPU cooler away.
Step 3: RAM
RAM comes in sticks/cards (pictured). Each year, the average amount of RAM computers have grows, because the amount programs need grows as they advance.
Step 4: Drives
Most computers have either a HDD and Optical Drive or SSD, HDD and Optical Drive.
These are devices that read CD, DVD, Blu-Ray, and any other disk you can think of. Almost all systems have them, because they are so commonly used. You probably know about CDs etc, so I need not explain them.
The hard drive is the predecessor of SSD, but is still much more available and used than SSDs.They are permanent storage, and can be powered down while still keeping information on them, unlike RAM. HDDs are made from metal disks, and function similarly to digital cassettes. Information is encoded, then written on to the platters using magnets. The platters are then read using a stylus a lot like the ones used on vinyl record players. Because information is stored all around the disk, HDDs spin around, and platters are very fragile
Solid State Drives
A very new enhancement. They function with 0 moving parts, and are a lot less fragile than hard drives. Information is stored in a similar formation to hard drives, but instead, SSDs have negative charged electrons and positive charged electrons. It's the same technology as usb drives, flash memory. It's a complex subject, worthy of it's own instructable. For now, I recommend http://www.howstuffworks.com/flash-memory.htm as a good source of information.
As technology advances, physical size decreases, and information capacity increases. The physical size for a hard drive in a desktop computer used usually now is 3.5". Laptops use a smaller size, 2.5". Most hard drives in mid range prebuilt computers now are 500GB, but vary all the way up to 2x1TB. Anything past that is usually a gaming computer, workstation or homebuilt
Step 5: Thanks!
The next tutorial will be maintaining and cleaning your computer. Keep an eye on my profile for updates