MotionFlow is a feature that uses the picture processor to insert frames into the content which are generated by and advanced UI, which effectively produces a smoother picture. In general, there are no "best settings" as it's a matter of personal preference.
I'd suggest changing a setting then checking if you like how the picture looks as an effect, or if you can even see any difference
Here's a description for what each setting does:
https://www.sony.co.uk/electronics/support/televisions-projectors/articles/00190409
