These are what are called piano accordions. Most accordions have this really cool boxy shape, also affectionately called squeeze boxes. Basically what an accordion is is a series of bellows that are compressed, pushed, or pulled and allow air into the instrument that crosses over a valve through a reed that then produces a vibration inside the instrument that creates the sound. So, by pushing or pulling I allow air into the instrument. Then by pressing a button the sound is created.
Many accordions have different reed options. This one in particular, this brand is called Main Squeeze, has five options for reeds. Starting lowest with the bassoon, the bandoneon, the master, the violin, and the clarinet.
On the left hand side of the instrument we have a set series of chords that are always the same on every instrument. Some instruments have a greater number of bass notes than others. This is a 48 bass. They go all the way up to, I think the standard is 120. There are some that are bigger, but those are really huge instruments. The 120 usually being the top that you would ever use to play. These are set up in a chord fashion with major, minor, seventh, and diminished chords. Major, minor, seventh, and diminished chords. The first row being closest to the bellows. The counter bass being a third.
It's a pretty cool instrument. Basically a one man band. You can play everything that you need to with both hands and accompany yourself on this instrument.