So, I'm starting a 3rd or 4th in house app today. They're all Swift4 using the latest version of Xcode. I have a big group of "Extensions" that I end up copying from project to project. This doesn't really scale in the end. So, starting a new app, I'd like to learn how one decomposes "support" code into a separate project or module or... I'm not even sure anymore.
There was CocoaPods which I was able to use, but never delved into. And then Carthage, same. And I know there's a Swift Package Manager, but I have no idea how that works or where to even go to figure out which parts to learn more about.
What is the basic roadmap (for a novice developer) to extract common code between 2 or more apps and manage that in a separate repository/module/package?