Scriptable Objects
Behind the scenes, much of the data in the game is saved as Scriptable Objects, which are a way to store information in an object-oriented manner. This makes the data intuitive to understand and also reusable. The Proposal Scriptable Object is arguably the most central to the game, and thus is a good place to start learning about how the game works.
To create a scriptable object asset, simply right click anywhere in the project
window and navigate to Create → ScriptableObjects → ...