Yea, I actually left that Autozone job to work in a warehouse that paid better money, thus started a trend of layoffs in the economic downturn. In hindsight, if I had stayed at Autozone the whole time at least I would still have full time employment, oh well. Coulda/shoulda/woulda.
As far as how to overclock a CPU, to keep it simple, theres only one way to overclock an Ivy Bridge, via the multiplier. There is techically another way to overclock a CPU at the reference clock, but Ivy/Sandy Bridge have very little tolerance for it, so don't do it. (The K on the model numbers denotes that its an unlocked multiplier)
The clock speed of your CPU is determined by the reference clock x the multiplier. For example on the Ivy Bridge 3570K the reference clock is 100mhz x 34= 3.4GHZ, you up the multiplier to 35 you get 3.5GHZ, and so on. You keep upping it and running stability tests until you hit a point that the system is no longer stable, or the CPU starts reaching max temps under load. You can technically increase the voltage to go higher, but this is where the real "risk" of shortening the CPU's life comes into play.
Although honestly, the risk isn't that substantial as it was back in 2000 for example. If you're really concerned, Intel does now offer an "insurance plan", for about 20-30 bucks that gives you a one time replacement should you fry a CPU overclocking it. However, barring doing something incredibly foolish, you'd basically be buying air.
CPUs are like snowflakes, no 2 overclock the same, but as a general statement you should have no problem overclocking a 3570K to 4.0GHZ, or higher if you feel "naughty". A lot of the boys on the forums here hit 4.5GHZ just fine.
As far as is overclocking necessary goes. Well, in my case no. I overclocked my Phenom II for no other reason than "because I can". A 3570K at stock speeds is powerful enough to take on any game on the market today. But then again, so is my Phenom II, sure the 3570K will give better benchmarks, and in the handful of games on the market that are more CPU intensive, there may be a noticeable difference, but these games are few and far between, and thats not likely to change anytime soon.
Overclocking is.. well look at it like this. If you're a car guy, does your car really need that fancy exhaust system that gives you 10 extra horsepower? Not really, but 10 horsepower is 10 horsepower. If you want your car to be slightly faster, then that means something.