Auto Layout Confusion

Hello throughout the book it mentions to use constraints to auto layout the text field or various modules but im confused what you mean. How are we supposed to know the numbers for the margins and the book mentioned if we add our custom constraints then we would have to add constraints for everything else. Can you clarify what you mean by utilizing the auto layout.

Auto Layout facilitates how controls respond to different screen sizes based on constraint assumptions. I don’t have the book available, but can recommend the following tutorial: