Its pretty simple, I recently built a PC and overclocked it.
basically you are raising the speed at which your CPU works (for example my I5 2500k runs at 4.8ghz instead of the stock 3.3ghz). If you want to overclock it would be best to get an aftermarket cooler as the stock fan will not sufficiently cool your CPU above 4ghz (even at 4ghz it runs pretty hot, in the 70 degrees).
Overclocking is pretty simple, I kinda guessed while doing mine, you simply change the speed of your CPU in the bios and the voltage. I found it easiest to leave the voltage at auto and change the speed to what I wanted. Then when booting up my PC I used cpu-z to check what voltage was being applied automatically by the PC then restarted, entered the bios again and gradually lowered the voltage until my PC became unstable.
To check whether your overclock is stable you can use Prime 95, run it for a while and if your PC doesn't shut itself down you have successfully overclocked, congratulations. before lowering the voltages from auto as i explained above check your CPU is actually stable at that speed with prime 95.
I'd also like to add this is a noob guide/explanation to overclocking but it worked for me, there are a couple of other settings you can change to allow you to achieve greater speeds but I will let someone with more knowledge explain. Basically what I explained above worked for me. Also don't expect to be overclocking much higher than 5ghz as each chip is different therefore some CPU's simply won't reach that speed stable. I read somewhere only around 5% of I5 2500k's (the CPU PP suggested In the above build) actually reach above 5ghz.
When you get your rig feel free to ask for help in the overclocking section of the forum. Myself and a few others on the forums have 2500k's and can give you starting points for your overclock and help you through it (for example I can give you the settings I am using at the moment to see if it works for you).
