Here are straightforward explanations of what each setting does and when to use it, as well as showing what Protune settings are available on which GoPros.
Some GoPros, like the HERO5 Black, offer a choice between two color modes in the photo mode: GoPro and Flat. Here are some examples and when they're best used.
Some GoPro models give you the option to choose between high, medium, and low levels of sharpening. Here are some examples to help demystify what these different settings do.