I have those strange buttons in my keyboard so I was wondering what are they for ? When I press on one of them, the leftmost notes output weird sounds whenever I play them I can't understand ??
I don't know what keyboard that is, but that looks like the control for the ABC [Auto Bass Chord] system [That's a Yamaha term, other manufacturers may call it something else, but they all do a similar job]. Basically, it's a chord recognition mode.
When set to Normal, the ABC system is off.
Whatever notes you play, that's what you will hear.
Fingered applies 'complex' ABC.
If you play C, E, G, B it will play accompaniment in CMaj7
C, E♭, G it will play Cmin, etc.
Some of these are pretty clever & can differentiate between, say, C6 & Amin7 depending on how you voice your chord. Some can't. Some can recognise right up to a 13th chord. Some can't. Some can make musical sense out of complex chords, for instance by applying priorities to root & 5th, 'flavour' notes below & above the octave etc… Some can't.*
S. Finger is Single Finger, 'simple' ABC.
In this mode, pressing C will play CMaj.
[This is where manufacturers may differ]
Pressing C & B will play Cmin.
Pressing C & B♭ will play C7
Chord recognition in this mode is necessarily limited to just a few types.
*Some of you may already know I used to make these accompaniments for a living. I am still under NDA & not at liberty to divulge just how this is all calculated. Sorry.