Conversion tracking allows you to measure the effectiveness of your AdWords app install and app engagement campaigns--by tracking the installs and in-app events (such as purchases and sign-ups) that were driven by your advertising.
Remarketing then allows you to reach existing users of your app with ads to re-engage them with your app, driving even more conversions.
It's common to use both tools together.
AdWords provides a lightweight app SDK for conversion tracking and remarketing.
If you are already tracking app usage and advertising effectiveness with an analytics tool and do not want to integrate your app with an SDK, we offer a server-to-server API option to notify AdWords of conversions and remarketing events from your analytics system.