Each Program can have one or two Osc, or oscillators, as the basic sound sources. One or two Osc are used in Single or Double mode, respectively. There are numerous multisamples to choose from as the basic sounds. Try loading a Program and changing the Osc, and see how the sound changes. The Osc output is then subjected to filtering and amplitude variations over time, and followed by effects, in order to produce the final sound. VDF is a Variable Digital Filter, variable over amount and time, and VDA is Variable Digital Amplifier (i.e. ADSR [Attack, Decay, Sustain, Release in synth speak]). EG INT is Effects Group Intensity, which specifies by how much an effects group affects the sound. If EG INT is set to 0, then the effects group have no effect, +99 is maximum effects group effect, positive, and -99 is maximum effects groupe effect, negative.
Since the M1 in the KLC is a faithful recreation of the original M1, the manuals for the original M1 are very much relevant, as far as the sound generation and modification capabilities go. Have a look at the resources here:
https://www.korg.com/us/support/download/product/1/139/
In particular, the M1 Original Owner's Manual, and the M1 Super Guide. These documents cover the internal sound-generating structure of the M1, AI Synthesis, and the Sound Making Process.
Other resources include:
https://gizmodo.com/a-beginners-guide-t ... 1736978695
And the M1 Software Synthesizer Manual at:
http://www.korguser.net/m1le/download/ - there is some overlap here with the materials in the other links, but that's no bad thing.
.