#1
i got my an Acoustic B450 combo amp , and i'm stoked as ****. anywho, the manual didn't do a good job of describing things to me and neither did google so i have two questions

1. I have a gain and volume knob, i know i'm supposed to get volume to desired level and then lower gain so it doesn't clip, would it harm my amp to turn the gain up so i can get a bit of distortion?

2. What the hell is the frequency knob for?...
#2
it wont harm your amp if anything thats what the gain knob is for
no idea about the frequency knob
#3
1. yes it would. i've learned from experience :P

and 2. its pretty much like a scoop knob is what i figured it to be. just mess around with it and see what sound you like best
Guitar Rig:
Fender Telecaster
Martin GPCPA5
Orange Rockerverb 50

Bass Rig:
Squier Vintage Modified Jazz V
Hartke HA3500
#4
From the specs you have provided: 6-band EQ with Sweepable Frequency Notch Filter.

A notch filter is a band-stop filter with a narrow stopband (high Q factor). Notch filters are used in live sound reproduction (Public Address systems, also known as PA systems) and in instrument amplifier (especially amplifiers or preamplifiers for acoustic instruments such as acoustic guitar, mandolin, bass instrument amplifier, etc.) to reduce or prevent feedback, while having little noticeable effect on the rest of the frequency spectrum.
Marshall amplifiers are the truest purveyors of rock and roll known to man.

"And give a man an amplifier and a synthesizer, and he doesn't become whoever, you know. He doesn't become us."

Holy crap, check this out!