One more try,
Russel,
Manuals of ANY keyboard are a pain in the behind any way.
OTS is a One Touch Setting and it set a variation of VOICES under a button choicen by Yamaha as what they think combines with the STYLE you’ve picked, best.
BUT if you don’t like the factory’s choice you can program them yourself and save the new OTS as you like in user area memory.
Do the following as example: Pick a style from your keyboard, you will see the OTS lights come on.
Start playing the style and something with the RIGHT-hand, now push the different OTS buttons, you will notice a different VOICE or combination of voices under each button. You can combine any of these OTS settings with any of the variations in the STYLE.
Auto Fill In sounds when you make a choice between the available VARIATIONS in a STYLE. Often they sound also when you push the same variation again while it is playing already. Gives it a bit more prof sound to the ‘backgroundboys’ in the band in the style you’ve picked.
Just try it, won’t hurt and you can’t ruin anything.
Don’t be shy and come back with your questions but most of all have fun with your keyboard.
DickR