In Intel's dictionary, a K version of a CPU means that it is unlocked. Unlocked means that with a compatible motherboard, you will be able to fully control and overclock your CPU as you wish.
Overclocking means to push your CPU out of the recommended operating frequency, it is a way to get more performance for the price that you've paid. However, overclocking does take patience and skill to accomplish a reasonable stable overclock. If you just want to have the PC up and running like it suppose to without messing with anything else, then I recommend you to not overclock.
In addition, as I've mentioned above that not overclocking can also save you some money on the CPU itself and the motherboard.