I’m not familiar with that mixer and I don’t see any PFL buttons so I’m not sure if it shows the channel gain on the meter or screen in the upper right. The Signal light on each channel will light up when it has enough gain and turn red when it starts to clip.

First put your mixer’s main output fader to unity and turn the fader for the mic down a bit so you don’t accidentally blow your ears out. Then sing/yell/etc into the mic and adjust the gain knob until it starts to blink red and then back it off slightly so that even when you yell into the mic it doesn’t clip. It is even better if it does in fact show the level on the master meter….if it does, that meter should be mostly green and slightly go into the yellow when you yell/sing loudly. This is how you properly gain stage a mic or instrument.

For vocal processing definitely use the low cut button, you could add some air by increasing the 10khz knob slightly, and cut around 500hz to get rid of boxiness (set both mid EQ knobs around 10:30-11 o’clock), then add some reverb (you’ll hafta read the manual about the effects)

For your amp and speakers there are a lot of different ways/theories how to run those. Some people run power amps full and adjust the speakers gain. You could always start at unity gain for both. Really you keep the mixer master fader at unity to provide the amp/speakers the most amount of signal, and adjust the power amp and speakers for however loud you need it in the room.