Overclocking is about increasing the speed of your computer.
What most overclocking get on a modern computer, get I would say at best 5% to 10% better. Often I have seen figures of 1% making it not worth doing. But anyway this is how it works. Computer manufacturer designs a computer with a specification. They then collect the components from many people and puts them together to make a computer.
Today what happens is that components vary, the manufacturer specifications are the minimum. So, for example, I have parts in storage that can do 100, you want 90, well if I do not have 90, so I may give you some 100s. Some many of these components are better then what was asked by the manufacturer. This happens all the time. We live in a world where we see components vary in the computers in the same production run.
Also, reputable manufacturer tends to underestimate many of their specifications, to cover themselves. Plus engineers tend to build to the lowest specifications.
Another point is that a computer designed as an all-rounder, to do a whole lot of tasks. Yet your computer only does a few jobs so may get your computer to run faster by turning off some functions.
So what overclocking does is try to run the computer faster then the processor is designed to do.
Now there was a time when you needed a lot of specialised knowledge to do this but any more. Overclocking software exists that does most of the tasks now. Check your system board and your supplier will have a piece of software that can do it for you.
But there is always at least one but....
Even if overclocking doesn't do any harm, it could still void your warranty. If you are thinking of overclocking a computer under warranty, you better check with your supplier first.
If you are doing a lot of data processing, most of the speed lost is in the hard drive and its severe bottleneck. So speeding up the processor often does little.
What you are doing is running your computer faster. This will reduce the life expectancy of your computer. This will also increase your computer's power consumption, which means more heat. So I do suggest if you overclock that you buy a better cooling unit for your computer.
Why do it, well overclocking your processor speeds up your computer. That's a pretty good reason.
You may as such keep a computer going for another year or so, and if you do it, you will find that its a lot of fun.
Make sure you do not kill your computer, so start with a "light" overclock. Say about 5%, try it out and see if it works for you. Then when you get the hang of it, go a bit higher but stop at 10% unless you know your stuff.
I overclocked my laptop. It works fine now, but I cannot run chrome on it for long. So I run another browser opera because otherwise, the laptop gets too hot with extended use. As I said, there is often a price to pay.