what does the term "overclock" mean?
The short of it, crank up the processor beyond its rated specification and crank down the memory timings.
To keep the processor within it's heat tolerance range, you need to improve the cooling over the stock coolers. Memory tends to need heat spreaders, which most quality ram has these days with an eye towards improved timings. You then make sure the case it's in is well designed to allow good airflow.
Some folks use water cooling on the CPUs, others still use compressors to get frigid temps to allow for some pretty extreme overclocks.
I tend to buy components that allow me to mildly overclock without any issues. I've not done it yet in either of my AMD 4000 machines simply because they've only been built for under a month and I wanted the Arctic Silver(CPU thermal "grease") to "set" and the machines to be stable before I monkey around.