Behringer BXL 1800 180 watt amp
 

Recently got a BXL 1800 and I'm trying to figure out something's on it.
1 It has a 7 Band EQ and it has a ****ing button that when you press it the red lights on the eq nobs turn off and the button yellow light turns on. *** does this do? It seems to not have any effect on the sound.
2 it has a compressor knob. What does this do? I turn it and barely head anything different.
3 Ultrabass knob. Now when this is on only sometimes I hear a difference.
1-a what's a good way to set the EQ up to get a nice low groovy sound? Any like presets?