Hey there @ColdEnd, welcome to the Discourse!
As @Simica_Na showed, you can see exactly what your Hearthlings are doing (or not doing) via the citizens menu. As for the exact AI, and priority list, you would need to install Debug Tools. The devs have been very clear that they do not want the game to be micro, so I’ll be honest and say that I doubt you will ever be able to fine tune an individual Hearthling’s AI beyond the citizens menu without a mod.
Edit: Looks like you posted while I was typing. Let me respond to that. Changes made in the citizens menu should not function as suggestions. If you disable a Hearthlings ability to mine (for example) they cannot mine. If you have noticed otherwise, that would be a bug.
As for standing idle, there are so many possible reasons why that can occur. When it comes to building, the most common is that the AI cannot determine how to build the structure, and thus does not appear to do anything. If you find buildings where that occurs, please save them as a template and upload them to the thread below:
http://discourse.stonehearth.net/t/the-buildings-my-hearthling-will-not-build-thread/14704/45?u=jomaxro