You can power the amplifier from 3-5V DC. If you want to use a wall adapter, a 2.1mm terminal block is handy
Testing the amplifier is really easy - no firmware or special configuration required to get a little audio out. In these images we'll assume you're using a breadboard but the wiring is the same if you soldered connections directly.
The easiest way to test your amplifier is to connect a 3.5mm audio pigtail cable to the audio inputs. Connect Right to R+ and Left to L+ then since a 3.5mm audio cable is single-ended, connect the ground wire to both R- and L-
You can connect the power to the board via either a breadboard rail with 3-5VDC on it (say from an Arduino power supply or battery pack)