This is my first lesson on computer building. Assuming you have read the introduction, I will continue verbatim.
Parts Assembly, is an important step in building a computer, however, we shall try to help you understand a little of what these parts are, and what you are doing with them first.
you may see a box much like this.
this is your motherboard.. its the template on which almost all of the other parts sit.
An important part is the Central Processing Unit also known as the CPU. In the upper center of the motherboard is a block, this block is called a 'socket'. There are two main manufacturers who make sockets. One manufacturer is Intel and an other is AMD. Each have different ideas how to make computers/cpus. Each work well and do not stop you using Microsoft Windows programs.
you need the correct CPU for the correct socket.. think of it like putting a key in a hole, or perhaps a jigsaw piece in place. if the wrong piece is forced, the computer will break.
There is also a 'latch' which looks like a lever, to hold the CPU in place. you must unlatch it to put the CPU in, and then re-latch it so the CPU is held tightly to the motherboard.
The CPU should come with a fan and heatsink, a large grey metal block with a fan atop it. it also has a wire to connect it to the motherboard, this wire is important, as it powers the fan directly from the motherboard. at some point it is important to connect the fan while assembly is taking place and before you have put any power in to the motherboard.
Here is what a correctly inserted heatsink and fan look like thanks to wiki!
The heatsink and fan sit on top of the CPU, and also the heatsink *should* have some gooey grey stuff on it, this is called thermal paste, its a grey very very thick liquid, to cool down the CPU, it bonds the CPU and heatsink together to make sure there's no gaps and so make it a little cooler.
Once the heatsink is in place, there should be a way of attaching it to the motherboard, there are too many different ways to go into detail here.. although the standard Intel and AMD 'stock' fans have two systems, latch and pop, AMD use a latch based system and Intel use a 'pop' based system. the AMD latch system is much like latching a garden gate. While the Intel system is 'pop and click'.
The RAM modules fit upon the motherboard also, they have two latches to each module and central notch that must be aligned.
here is picture of two correctly installed modules.
this concludes the first lesson.
Introduction : http://www.overclock.net/a/how-on-earth-do-i-build-a-computer-beginners-guide
Lesson 2: http://www.overclock.net/a/how-on-earth-do-i-build-a-computer-lesson-2
Lesson 3: http://www.overclock.net/a/how-on-earth-do-i-build-a-computer-final-lesson-3