I'm a total beginner and I can't understand much, well, I know it is a theory. But don't worry I'll try harder and think harder haven't finished lesson 1 yet. 
Hi PECO,
A beginner might be better served by a very simple explanation of How an amplifier circuit works then those lessons will make a little more sense.
This might be really obvious to the Teck minded but to a novice they need a *concept*.
This helped me a great deal.
Without a concept you will likely get lost in the maze,, heck I did

Simply put; Just *AC Volts riding on DC Volts*
An Amplifier is the AC wiggle of the guitar string (or any musical signal, the stuff you hear)
and it rides on the DC potential created (setup) by the DC Voltages of the amplifier circuit.
When looking at a schematic you are looking a *Two quite separate circuits*;
First you have to DC Bias the Active Elements so that the AC signal can pass through
and hopefully be Amplified by the Active elements without passing needless DC current
through the active device which will just be wasted and may even burn out the device.
So you need to set up the DC conditions of the amp (bias) then you tweak the stuff you actually hear, AC signal.
If all goes well the AC signal output will be bigger than the AC wiggle going in hence it *Amplifies the signal*
So straight up you NOW know you are looking at 2 circuit paths when viewing a schematic.
There is an AC path and a DC path.
Also there are DC currents and AC currents not just voltages.
When a big power Amp blows up it will usually be a DC related problem as these pass big DC
currents and if not biased correctly will burn out big transistors in spectacular fashion.
Try and stay away from all the Thevenin,Norton Equivalent stuff until you grasp some basic transistor circuits.
for the average joe who wishes to build a few pedals it's needless complexity.
Does that help?
Phil.