Ultimately I would like to assemble this simple audio amplifier:
Given my lack of any significant knowledge in the topic I have several problems and questions.
In the thread What is ground and what does it do? it has been said that grounding is basically about creating a reference point and:
Remember, a complete circuit is required for current to flow. You would need connections to earth ground in two places for current to flow in and out of your circuit from earth ground.
Let's take a lightning. If I am struck by it, how come the circuit is closed? The current certainly flows through me. And also if there was no current flow through grounding wire in any case, what would be a physical reason for attaching it?
In the schematic I showed there are signs of earth ground in multiple places. I saw some video of a man creating this amplifier exactly and it seemed to me (the footage is not that precise) that he created a stand alone device, therefore there could be no physical attachment to actual ground by any external wires. How then should I understand the grounding symbols?
In the LM386 data sheet I found a statement that it features "Ground referenced input". How am I supposed to understand that? Also about pin number 4... Should I attach the pin to the ground (as possibly shown in the schematic) or I could attach all the wires ending with the ground symbol to this pin? If it's the latter how is the pin constructed inside the chip? How come it serves as a ground?
I have already assembled some amplifier that looked more or less (rather less) like the one shown. The problem is that it worked with an input from a regular PC jack but it did not work at all with an input from 2.5 mm telephone jack. Someone said that it's because PC audio already has boost and the telephone's port does not. Did he mean a power booster by it? Like "push–pull output"? But what is the general difference between push–pull output and this amplifier? I mean, in this case I am trying to increase voltage of the signal and, as I understand, also a power output (P=UI=U^2/R). So I need a booster to boost my signal so I can boost it again? I don't understand. Someone also said that it could work if I assembled my amplifier correctly. If I assemble this very circuit correctly without any additional parts, will it work with the telephone jack I mentioned (Panasonic KX-DT333)?
Also what is the function of the 0.05 mOhm capacitor? What happens if I use 1 mOhm? Also there should be no problems if I use 220 instead of that 250 one, yes?