Yes its good but just make sure you're actually overclocking with that processor as it costs more for the K model.

The motherboard is total overkill, you could get the most out of the chip with overclocking with one for a fraction of the price.

My friend that set these parts up said we weren't gonna overclock

Well if the system is for you then the choice is yours. But if you think you wont overclock for sure then the i5 4570 is cheaper and will perform the same, and you can use a B85 motherboard to keep costs down.

Well I want to be able to run dayz and other games really good, should I overclock? Will it be a big difference?

No not really. With the money saved from not getting the K processor and cutting down on the motherboard you can probably get a GTX770. The graphics is most important for gaming.

What other parts will I have to get if I want to overclock

You'll need the K model i5, a good motherboard but one thats cheaper than the one you picked as its overkill. You'd need a cooler for the processor, and also a case that could handle the height of the cooling tower, or the radiator size. Lastly a decent power supply to power all of the components.

I don't know much about this but how does overclocking work? And can it affect your computer in a bad way?

Essentially you run the processor out of manufacturer recommend specification. Its usually not covered by warranty.