I need help with audio amplifier project

Nothing to do with "Arduino" or coding:
I need help with learning audio amplifiers.
Just a simple project. I wanted to amplify the sound from a stethoscope just for fun.
I have:
Adafruit PAM8302 item #2130 for amplification
flat 25mm Piezo with 2 wires (red,black)
2 other audio microphones which have 3 wires. Assuming red and black are for + -, the yellow wire for audio out.

Would the yellow wire be digital or analog or does it matter?

Can I hook up the piezo directly to the PAM8302 board? Which Pins?
The other 2 microphones, which pin for the yellow wire?

I'm asking here because I see this sort of thing being used on musical instruments and not sure where else to ask