C1 is the input coupling capacitor - it blocks DC voltages and passes AC.
C2 is a decoupling capacitor. Frequencies above 5 Hz should be decoupled.
R1, R2 and R3 are used to bias the MOSFET to get the correct DC potentials in the circuit.
R4 is a load resistor.
C3 is the output coupling capacitor. It passes AC to the speaker and blocks DC.
The biasing should be adjusted to give a MOSFET drain potential of 6 Volts with no input audio.
There is DC negative feedback to keep the biasing correct. The AC feedback is decoupled by C2.
The drain current will be I = V / R = 6 / 10 = 0.6 Amps.
The MOSFET and R1 will each dissipate P = I V = 0.6 x 6 = 3.6 Watts with no input signal.
Advantages
No cross over distortion - potentially better audio quality.
Some audio enthusiasts believe this type of circuit is worthwhile in spite of its disadvantages.
Disadvantages
It's not energy efficient. 7.2 Watts of heat are produced even when there is no audio output.
A push pull amplifier dissipates almost no energy when there is no signal input.
A bulky output coupling capacitor is needed.
Large heat sinks are neeed to remove the waste heat.
