Installing GammaRay is described here. If you are a user of the Qt Automotive Suite, you can skip this step as GammaRay comes pre-installed with your SDK in that case.
In order to start using GammaRay, familiarize yourself with its Basic Operations first. Based on your preferred workflow and user interface you can dig deeper in the following chapters:
Learning GammaRay's Capabilities
Once you can operate GammaRay and use it to interact with a target application, there are additional resources to learn about the capabilities GammaRay provides you: