Two ways you can learn what EQ does in detail:
---Plug your bass into a graphic EQ before your amp, and move all the sliders up and down and listen to what they do. If you don't have a graphic, a parametric will work, but it helps you get a better idea of the different freq ranges if it has shiftable frequency centers.
---Record your bass into a computer, then run it through a graphic EQ plugin and move its sliders up and down and listen through a decent set of headphones.
If you're just trying to get a good sound out of your amp, start with all knobs in the flat position and all tone switches off, then turn knobs until it sounds good to you.