Document on-boarding process and user flow from install to first message for mobile messenger apps

We are working on a mobile voice messaging app. We want to collect data on how most successful messenger apps onboard new users and engage them to start using the app. Documentation should cover all the steps from the moment user downloads and launches the app for the first time to the moment where the user engages is engaged to write a first message or to share the app with friends/family who don't have the app. Need to consider different user scenarios: 1) User installs the app and doesn't have any contacts within the app. 2) User installs the app and sees some friends who have already installed the app. In both scenarios, we need to document how does the app push the new user to engage in the app. iOS Applications to review: whatsapp telegram viber wechat line kakao talk Documentation should be in a user flow format with screenshots.