You can actually read a lot of this in the manuals.
If you read section "2.9. Part Controls" in Keylab Essentials manual, then you can see, what "bank" means. It's used with the DAW map. It's about how the next/ prev act in 2 modes.
When you use the Analog Lab map, then it's part 1, 2 and live tab selectors.
If you in the Midi control center (MMC) select the Keylab MKII device, then you can see, that each encoder and fader have 3 tabs for the 3 banks Keylab MKII have. This the Essential does'nt have.
Regarding the settings you have in MCC for the part 1, 2 and live buttons:
- I think "OFF", then it's simply working "normal", meaning like the labels on the keyboard show.
- When you use MIDI note, then you can send out a midi note instead.
- When you use Switched Control, then you can send out a midi CC messages.
- I don't understand why they use the name Patch Change, as it's actually is a ProgramChange message, that is send out. ProgramChanges include both a Bank and a ProgramChange value. It's used to select a preset or patch like some call it, and that might be the reason to use the word Patch, but i think they should call it Program Change.
https://en.wikipedia.org/wiki/General_MIDI- When you use MMC, then the buttons can send MIDI Machine Control commands.
https://en.wikipedia.org/wiki/MIDI_Machine_Control