I want to connect Adafruit PAM8302A amplifier to the Raspberry Pi 3 Model B+.
What I need? How to do this?
If you scroll down that page you linked to, in the learn section there a quite a few projects that use that board with the raspberry pi. One of them includes these instructions:
PAM8302 Audio Amplifier:
GPIO #1 (3V) on the Pi connects to VIN on the PAM8302. GPIO #9 connects to GND on the PAM8302. The +Postive and -Negative connections are wired to the A+ and A- on the PAM8302.
The Audio jack plugs into the audio port on the Pi.
Looking through some of the others should be helpful too.