Q:

What does "Sync Project with Gradle File " really mean?

In Android Studio there is a button Sync Project with Gradle File， I always use it, and it's useful. It will download dependence packages and maybe something more.
But what does it really mean? 
Is there a corresponding command in gradlew?
If I develop an app just using gradle, NO IDE, what commnd should I use ?

A:

The button does what it says: it updates the Android Studio project model to match the contents of the Gradle build file.
There is no corresponding gradlew command because there is nothing to synchronize when you work with the command line directly. The dependencies will be updated automatically when you run other Gradle commands such as compile.

