Well, there are many types of EQ. But normally for recordings, we usually use the parametric EQ found on most audio console to do a quick mix. And in todays recording studio, most are using hard-disk based recording systems, where you straight away record into a DAWs like eg., Protools. And normally, mixing are done using EQ plug-ins, can also say it's software EQ. But according to what you describe, I assume that you are toking about those hard-ware rack-mounted EQ units, with alot of different bands of frequencies avaliable for you to adjust. Those are call Graphic EQ. And normally those are used for tuning your systems to the room so as to achieve a flat and accurate monitoring response.
Just for further info if you interested:
Well, in studio, what you want is a accurate and flat-response so that it won't boost or cut any frequencies from your sound, and hence, you are listening to the exact original, uncoloured sound. From here, you are able to listen to which are the problematic frequecies to cut off, which to boost. This is why when we are purchase a studio monitors, one actually is looking for monitors with flat-frequencies responses as possible.
But the problem doesn't solve here yet even if you bought a flat-responses monitors. Don't forget different room will boost and cut certain frequencies range due to their different dimensions of the room. And this is why you need to tune your system to the room. First step is of coz you need to do some acoustic treatments like using foams or something to aborb sound.
Second step, plug your main audio out from either your sound card, or from the mixer if you have one, into the EQ audio in. Then plug the EQ audio out to your monitors. Which mean the audio signal will passes thru the EQ firts before going to your monitors.
Third step, place a mic in the monitoring position and connect the mic to a spectrum analyzer. Then playback pink noise thru your monitors. The mic will pick up the sound and you will see a waveform representing your current monitor's frequency response in that room. By rite if you insert pink-noise into a spectrum analyzer, you should see a straight line. But due to the room characteristic, it tend to boost or cut away certain frequencies, hence, making your monitoring response un-flat. And this is where the Grahpic EQ comes in. See from the analayzer which frequency is being cut or boost and adjust the EQ according until you see a flat response on the analyzer.
This is normally the remaining job what hardware EQ are for in todays software-based studios. I'm toking about studio, and not live-sound, so dun mix up. Coz studio n live sound are abit different to some extent.
Lastly, pls bear in mind that during mixing stage, EQ are used more for cutting away purposes than boost. Boosting using EQ should only reserve until the last resort. Enjoy and have fun.