I guess @Nir might chime in with more information.
An Equaliser as the name implies provide number of “elements” (bands / filters) to cut/boost an area within a frequency.
First a quick reminder:
EQ should compliment a good recording (sadly, it might also be used to fix a bad one but it is always suggest to make your recording great by mic position and good performance prior to EQ-ing).
So let’s say you’ve got a vocal. and you’d like it to be more “open”. it depends on the context but you might wanna cut some low/low-mid or boost some highs.
Let’s say you’ve got a bass. if you’d like it to be more “bass” you’d might wanna cut some highs or boost some lows.
Bass and vocal are great starting points (especially with SurferEQ & SurferEQ Boogie )
I’d suggest reading online about EQ usage of course.
What makes SurferEQ (and SurferEQ Boogie different):
Most equalizers are assigning each band to a specific frequency.
SurferEQ allows you to benefit from pitch-detection and “move” the frequency harmonically with your audio content. Try playing with SURF mode on a vocal and bass.