This site summarizes Google's recommendations for webmasters who want Google Search to index and deep link to their native mobile apps.
What is app indexing?
App indexing allows you to connect pages from your website with specific content within your smartphone app. This enables smartphone users who have your app installed to open it directly from relevant mobile search results on Google.
For example, imagine you run a recipe website and have an app that can also show your recipe. Thanks to the app indexing feature, when a Google searcher on a mobile device is shown one of your recipes as a search result, they will now be able to open that result directly in your app if they have it installed.
This search feature is available on searches done using Google Search App version 2.8+ for Android 4.1+, and in mobile browsers on Android if the user is signed in.
Currently, app indexing is enabled for a group of initial websites and apps. We're working hard to bring this functionality to more websites and apps in the near future. You can: