It is hard to navigate and there’s lawyers and accountants who make a lot of money figuring that out.
I interpret it as directing work as a supervisor would exert “behavioral control.” For employees you control behavior. For contractors you control outcomes.
So if you give a step by step plan on how to prune to your gardener and require it precisely, that’s probably a contractor. If you require that he prune the bushes and don’t care how it’s done, then that’s likely a contractor.
I used work with programmers quite a bit. There are a few tests where you shouldn’t provide exact tools, set break times, set specific hours, exclusivity of work, require methods of pay for contractors as that is only possible with employees.