Update Frames & Constraints in Xcode (Interface Builder)

I'll try to explain the concept of constraints and storyboard representation.
Constraints - are used to determine the position of UIView elements inside your view. For example, the vertical distance from top of the view to UIView element top. When you add constraint using the storyboard it plays 2 roles:

1. Positioning the element inside a view when your app runs
2. Positioning the element in the storyboard representation itself

Update Frames - is used when you want to update storyboard display so that it fits the currently applied constraints. When the display of the storyboard does not match the constraints a warning will appear.

Add missing constraints / Update constraints - will create/change the constraints applied on UIView element to match what currently presented in the storyboard. Kind of the other way around from update frames.

• This answer is not a replacement for Apple's Auto Layout Guide

You do not have to click on "update frame" every time you add a constraint, if you do, it will update the frame of the view to whatever it should be based on the constraints. Yes, every view has a frame and it is the rectangle relative to the views superview.

More often than not you'll probably click on update constraints (Shift + Command + =), this will allow you to resize views that are already constrained, and have the constraints updated to match.