Basically you've got a 7-band EQ. Each bar centers on a frequency a little more than double the one before. That puts each bar a little over an octave (in musical terms) above the one above it.
What the bars do is change the "shape" of the output wave, emphasizing where the sliders are higher, softening where the sliders are lower. They affect each other, to a certain extant. If you really slam 400hz all he way up, you're gonna see a slight increase in the adjacent bands as the 400hz band stretches upward.
Most natural sounds are in the 100hz to 400hz range. Even 1000hz, which doesn't seem like much when you can go to 20,000, is a pretty high tone.
What the higher octaves give you are what audio folks call overtones, where devices that make sound will resonate in higher frequencies over their base (not bass) tone. Missing highs (and extreme lows) makes music sound flat and dull, like AM radio or telephone sound.
The point of the EQ is not so much to modify the sound, but to correct for room acoustics. If you've got a lot of drapes or certain floor coverings, highs may be absorbed by the room, making life dull. You also want to de-emphasize frequencies where the room is resonant, because sound at those frequencies will sound boomy.
These days EQs are used more for overcoming crappy speakers. If you had a budget of say, 2000 dollars for a sound system, you should buy speakers that cost $1500 and use the rest however you can. Speakers are the part you hear, and cheap speakers just can't be fixed.
Most people like a slight emphasis in the extreme highs, as it makes the "tinkly" things like cymbals, bells, etc. sound crisper. A lot of people assume you need more bass, so they slam the bottom one or 2 sliders all the way up. Your EQ doesn't even reach the frequency for that, though. 63 Hz is not deep bass, it's close to the background hum you get in an AC transformer or flourescent light. Pumping that up will just make your music sound muddy.
Most mass-market speakers these days could do with a reduction in the 200-400-hz range, and a bit of boost at the upper ends.
As for what fits the ranges, 63 is actually upper bass, more of a baritone. 160 is probably a male voice, maybe not even an especially deep voice, or low orchestral and band instruments. 400 is the mid-range, female voice, etc. Consider that the A above middle C on a piano is 440 Hz. 1000 and up is where the overtones live, the resonances that give sounds their character. That's also where non-natural sounds may be found, like electronic music or effects. Adjusting the upper 3 or 4 sliders won't affect the actual instrumentation, but it will affect the sound quality.
