Adding Sources for more informative documentation
In IntelliJ/Android Studio, you can view documentation (e.g. JavaDocs of Android API) of code by moving your text cursor to the object of interest and pressing Ctrl + Q (WindowS) or F1 ( macOS).
However, in the default installation, the information you see is not super descriptive. To get more information ( description of the behaviour and purpose of methods, for example) you need to install Android Sources for your API version, which you can do in the SDK manager, see below screenshot:
After installing Sources, the documentation tooltip will look something like this:
