I want to understand this audio input to LED output simple circuit
C1 passes audio from the microphone to Q1 base while preventing the DC supply to the microphone from interfering with the DC bias on the base of Q1.
The +9V (positive battery terminal) should be connected to the top of R1, R2, and R3, and there should be a resistor between the top of R3 and D1 to limit the current in the LEDs.
I expect the -9V label is the negative terminal of the battery - it would be better to call that terminal &quot;Ground&quot;.  The +9V and -9V labels imply an 18 volt supply.