1) Gradle is a build tool, but it requires specific plugin to work.
Android Tool Team is releasing the Android plugin for Gradle.
com.android.tools.build:gradle:0.6.+
com.android.tools.build:gradle:0.7.+
com.android.tools.build:gradle:0.8.+
Here you can find the repo:
https://android.googlesource.com/platform/tools/base/
The current dev branch is idea133
. Otherwise you can check gradle_0.8/gradle_0.7
branches.
2) There is a relation between gradle-plugin and the gradle version.
For example
com.android.tools.build:gradle:0.6.+ -> gradle 1.8
com.android.tools.build:gradle:0.7.+ -> gradle 1.9
com.android.tools.build:gradle:0.8.+ -> gradle 1.9/1.10
You can find gradle version used in your project in the file gradle/wrapper/gradle-wrapper.properties
Also there is a relation between gradle-plugin and the IDE version.
For example:
Android Studio 0.3.x -> gradle-plugin 0.6
Android Studio 0.4.x -> gradle-plugin 0.7
Android Studio 0.4.3+ -> gradle-plugin 0.8
For updated news you can check this link: http://tools.android.com/recent
You can also check this updated post:
Android Studio Gradle issue upgrading to version 0.5.0 - Gradle Migrating From 0.8 to 0.9 - Also Android Studio upgrade to 0.8.1
If you change your plugin version, check compatibility, and then click sync project with your gradle files.It will download a new plugin version if you need it.