I’ll mention that if you are building a new iOS 12+ app and you plan on using Swift, you may want to consider using the Parse-Swift SDK. Both will work for iOS development, but Parse-Swift has more querying capabilities along with many other features (certificate pinning, 0 dependencies, etc.). On the flip side, the iOS SDK has been around longer, battle tested, and supports local storage directly (but has some known issues with this). With Parse-Swift you will need to implement local storage via CoreData or whatever other local DB you prefer.
Sign up examples as well as many others are in Playgrounds:
The API documentation can be found here: ParseSwift Reference