You'll need to power your amplifier with a nice supply of power! If you're powering from a wall, check the 5V 2A supply connected to a 2.1mm terminal block
For battery power, a 3xAA battery pack will do well, and can power your amp for at least a couple hours. You can use rechargeable or alkaline batteries, just keep your battery power under 5.5VDC max.
You can adjust the gain on the fly, at any time, by flicking the DIP switches. Start with 6dB setting and adjust up until you have the max gain without any distortion or clipping
The outputs of each channel are "Bridge-Tied" with no connection to ground. This means that for each of the two channels, the + and - alternate polarity to create a single channel amplifier with twice the available power.
However, that means you cannot bridge R and L together, so don't try to connect ROUT to LOUT, it will damage the amp! If you only need one speaker, just connect to either ROUT or LOUT and leave the other output set alone
Connect your speakers using the 3.5mm screw-terminal blocks:
Using the amplifier is really easy - no firmware or special configuration required. 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)...