First of all you need to study the model-view-controller design pattern to understand the why we need to create model class to hold the data and passing the data around view controllers.
Model-View-Controller is key design pattern in most of the languagesModel-View-Controller
Properties is the design pattern in objective c and swift which is helpful for sharing data among classes.
Properties in ios
I suggest you to study all the design pattern which help you for understating the objective basic
ios Design Pattern