Basic theory.
Humans can only hear from around 20Hz to 20000Hz although lower frequencies can be "felt" in most cases. Also as we age that upper limit shrinks (mine is around 17000 if I am lucky) and different frequencies can be heard more easily than others (1Khz to 4KHz probably being the easiest to hear).
Those sliders amplify the frequencies they represent although note that they are likely a log scale of some form (the first few will represent a few hundred Hz difference while the latter will be a few thousand).
Different styles of music then have different frequencies (notes) that epitomise the genre, by amplifying the given frequency you can make it sound "better" (in essence by drowning out the noise).
Alas we then run into the wall associated with a lot of audio science which would be the so called religious argument (I do not care what your test say "I" can tell the difference/think it is better) or the purist argument ("music should be as it was recorded"). Even very respected members of the community can be drawn in by these.
Secondly we have to worry about clipping. For the uninitiated clipping is a general signal theory problem that appears in sound as well, it is concerned with the waveform when being amplified will ultimately reach a point where it will no longer be amplified and the surrounding waveform will then continue to be amplified and the difference between the tones will become less and less resulting in a very "flat" sound.
In the end I suggest first trying the bass: low frequencies (typically under 100)
human vocals: they cover a lot of frequencies (think Barry White vs an female opera singer), this would be the 1KHz to 4KHz range for the most part.
upper limits are for things like guitars and keyboards (a staple of modern music).
Ultimately though this will mean little, I find most people respond to clarity, bass and a very minor echo (appearance of a large room) and at a more basic level if it is louder without hurting (much) it is generally "better" than an otherwise identical piece of music and none of those can reasonably be accomplished by an equaliser.
