Additionally to Uwe Stegers Video-Demonstration we want to mention the meaning of the coordination of both hands, which cannot be practiced on a laptop, but only on the vertically held pc keyboard:

Very many pieces of music use just the following three components::
1. Melody in a major- or minor scale
2. Accompaniment with mainly three chords: tonic, subdominant, dominant (T,S,D)
3. Rhythm.

It's not always easy to perform these three components together in a convincing manner.
For this reason the musical instruments should at least make it as easy as possible.
The cultural state of a civilisation is also represented by this quality of it's means!

Beneath organ and piano the accordion is an instrument that provides the means to play melody and accompaniment by one person at the same time. Accompaniment usually also provides the rhythm.. Stradella-Bass in the Circle of Fifths makes accompaniment on the accordion much easier than on the piano, because on the accordion T,S,D are always located beneath each other, no matter which scale is accompanied. You always play them in the same way with the left hand. For that reason the accordionist learns: Whatever sounds similar will be played similar, no matter in which scale. You don't have to practice these basics more than necessary and can focus on more important or enhanced musical aspects!
Like the left-hand-played accompaniment, the right-hand-played melody is able to amplify textual statements of meaning. But while accompaniment layout is sorted by the distance of fifths (7 half tones) and always "circles" in the same octave area, melody usually flows over more than one octave and is layouted on the instrument by the distance of just one half tone to its neighbor key.

This "progress in semi-tones" on the accordion can be layouted in different ways, like the applets in this chapter show. The best Layout should be similarly intuitive as it is for the left hand. For that reason we think 6+6-accordion would be the best choice for human fingers and mind. The only disadvantage is, that nobody produces it for the masses.

Practice left-right-hand-coordination with the different systems:
For piano- and 6+6-accordion the 4 Rows (2 for bass and 2 for melody) of your pc keyboard are completely sufficient to practice the basics. The additional rows on the real accordion are not that important for beginners.

For button accordions (on the right hand) unfortionately there's only one row left for the left hand, which is a bit poor for coordination practicing, but still possible.