The App Store gives you some information about your shipping app: the number of downloads and updates, user ratings, app rank, and a few more metrics. But the data can be hard to consolidate. And it does not tell you much about what users are doing or whether they are coming back to your app.
There are a few key questions in tuning your app:
Are people downloading and using your app (first-time use)?
What is the typical time using the product (engagement)?
Are users staying around (retention)?
What features are they using and not using ...