The Offline Mode is not really a feature, but it allows your users to download the contents of the app on their phones so that they can access it later, even if they have no connection. Let’s see how this works. When the users download the app and open it for the first time, they will be asked if they want to download the contents to access it when they are offline. If they do it, they will be able to access all the contents that are in the app even when they have no Internet connection.
But you have to know that everything that is linked to an external website will not be downloaded, like for example Youtube videos, Instagram galleries, or Facebook pages. As your users have to get the content from outside the app, they need an Internet connection to access those content.