While a good answer already given, I approach this a little different. (I would not turn the amp to full volume as step 1 for instance, nor would I raise the gain at step 4, as I would set gain in the gain structure, not to be used of ringing out a system)
First of all, I would set a good "gain structure" in the mixer/board.
This to ensure adequate head room for signals and not to amplify (or trying to avoid to amplify) noise.
While I can describe in detail how I set gain structure, a good video exists here
(I have no affiliation with video or creator of such)
Once you have set a proper gain structure, you need to ring out the system. There are usually 2 amplified systems in use, one: "monitors or foldback", and two: "Front of House". Again, there are video's which are much better in explaining this then me typing some text:
As you have described that you are in a church, I actually found this
There are many resources on various websites, both video and text, I would advise to search around.
[EDIT -- after some thoughts]
The title of the post lists a question, which was not answered yet.
Practical difference between channel gain, fader and amp gain
In a typical desk, there are a couple of places where "gain" can be set.
- The "Pre-Amp gain", usually found on top of the channel strip (but not always)
- The "Channel Fader", usually found at the bottom of the channel strip
- The "Group Fader", usually found between channel faders and master fader
- The "Master Fader", usually found at the right of the desk.
Larger desks/consoles will have different layouts, and obviously manuals should be read on how to use the various desks, this is only a general explanation.
What to use them for (practically as the question is)
The Pre-Amp Gain should be set, so that
- the channel is the only channel in use
- the channel fader is set to 0 dB
- (if used) the group fader is set to 0 dB
- the master fader is set to 0 dB
then the loudest possible passage of the input signal should not exceed 0 dB on the output meters.
This is setting the "gain structure", optimum signal path, optimum pre-amp gain. Although not mentioned, the [PFL] feature is implemented on many desks which makes this a lot easier to do.
"but what are all those faders for"
To put it simple: to pull back the signal, or attenuate the signal in your mix, to format the end result
- to pull back a single channel, pull back the channel fader
- to pull back multiple channels, assign the channels to a group, assign the group to main, and pull back the group fader
- to pull back main (to lower the volume), pull back the main/master fader
There could be other faders and features on any particular desk, and I would advise to always read the manual, and to have a good look at the block-diagrams to ensure you understand how the signals are routed through your desk.
"but what about the "amp gain""
One of the practices is to set the "amp gain" to the loudest level needed for the venue (estimate noise of people when the venue is full), at a 0 dB output of the desk. This way you can "pull back" with the main/master fader of the desk.
"ah now; that is just all theory, it doesn't work like that"
No, theory and practice are two different things, sometimes you just need to push a single channel a little more, hence when the gain structure is set at a 0 dB level, most desks have room on the fader slider above 0 dB. You do need to realise this is all in dB, so push a fader from 0 dB to +3 dB means double, to +6 dB is four times.
If you find that you are pushing channels during a live show, then you need to learn from this, something in your sound-check did go wrong. I have made many mistakes over the years, and only by doing you learn how to operate this more efficiently. I still learn everytime, no two situations are the same!!
But for what this goes:
- "gain" to push signal to 0 dB,
- "faders" to pull-back and create your mix,
- "main/master fader" to pull back sound level,
- "amp gain" to set maximum sound level needed for the venue.
.... usually it is better to pull back, then to push up: avoid clipping distortion and stay out of maximum ranges of op-amps and circuitry.
And from there it will only get more complicated when you start using inserts, compressors, limiters, gates, various effects, EQ, feedback destroyers... you get the picture...