Ask HN: building a Swift lib on iOs

Hi all, I am a pretty decent swift hobbyist with a few apps under my belt. I am now founding a startup where I will need to kickstart a project with more professional standards, and I am having a hard time structuring my code in a proper way, despite having spent a good amount of time on tutorials etc. I would like to isolate a core functionality of our app in a standalone "library" (starting from scratch), and can't get my head around it. Do you know of proper tutorials / resources on how to do this ? I feel like a lot of resources found on the internet are good for learning how to "hack" things, but now I'm at a stage where I need to do things the real proper way (i.e. money is at stake). Many thanks