Google is your friend. Search "overclocking i5 750" and get flooded in guides, pick one from a reputable site and read
If you
really need the pure basics, your speed of the system is made by the clock generator, and for your rig it's 133mhz. There's a cpu multiplier, so the cpu can run at a multiple of the system speed. Intel has locked the multiplier from changing, so the way to overclock is to increase the system speed (aka bclk/fsb etc...). The only problem with that is that all the other speeds go up as well because they are also based on the bclk, such as memory, northbridge, qpi... as you can tell from my nooby-ness, I don't own a nehalem

but the general idea is there, you'll have to lower the multipliers of everything else to keep them at reasonable speeds... hope you're not confused yet