Ionic Storage 3.0 does not have ready anymore, so you may have resorted to a tutorial of a different version.
Storing the setting across sessions (so after app closure) - here you can use the local storage or push to a server. Whatever your use case is.
Using localstorage to persist data across pages is technically possible but undesirable. Here Angular has defined the concept of a service. Maybe best for you to check the tutorial on angular.io to learn the basic architectural elements.
Where soon after you find yourself figuring out how to deal with lifecycle of compont and updating data across your app. When you start meddling with lifecycle hooks for getting data, then it is time to learn about BehaviorSubject instead. And this forum has lots of info about this (read: people struggling with the acceptance of their async fate)