As with websites, there are two basic categories of user interaction you can track: pageviews and events. Since mobile apps don't contain HTML pages, developers simply determine when their apps should trigger pageview requests. Google Analytics then aggregates this data in the Content reports to display the number of visits, session length and bounce rates. The data gives insight into how your users interacted with the app.
Developers can also track visitor actions that don't correspond directly to pageviews using Event Tracking. These user actions can include views of embedded videos, button clicks, downloads and more. App developers can then use this data to understand which features are most popular and inform decisions about which features should be promoted or prioritized for further development.
You can learn how to integrate Google Analytics into your iPhone apps at the link below...