Hello, welcome
The object of overclocking is more speed, kinda like hotroding a car. There are various ways to improve your computers performance one of which is "Overclocking your CPU"
CPU speed these days is measured in gigahertz(ghz) example Intel C2D E6600 runs 2.4ghz which is derived by multipling the CPU bus speed x the CPU multiplier, for the E6600 that is 266x9=2394mhz or 2.4ghz. You overclock the CPU by increasing the FSB or the multiplier(multi) in bios, however only top of the line extreme chips have an unlocked multi so overclocking non-extreme chips is limited to increasing the FSB.
The risks to hardware through overclocking is vastly overstated as long as reasonable guidelines are followed. The real risk in overclocking is lost or corrupted data including critital operating system data, which can cause you to have to reformat a drive and reinstall Windows(worst case), but this too can be avoided. Overclocking invovles increasing the speed in small steps and testing for stability, and your final overclocked settings must be tested throughly for stability. Once you have throughly tested your system stability the risk of data loss or corruption are about equal to a non overclocked system.
For these reasons you should always back up all your data before overclocking, and I recommend overclocking a fresh install and throughly testing stability before loading programs and data on new builds