You will generate them once, but update them if you need a new feature or something from a plugin which in turn needs a newer gradle version.
Easiest way to update: as of Gradle 2.2 you can just download and extract the complete or binary Gradle distribution, and run:
$ <pathToExpandedZip>/bin/gradle wrapper
No need to define a task, though you probably need some kind of build.gradle
file.
This will update or create the gradlew
and gradlew.bat
wrapper as well as gradle/wrapper/gradle-wrapper.properties
and the gradle-wrapper.jar
to provide the current version of gradle, wrapped.
Those are all part of the wrapper.
Some build.gradle
files reference other files or files in subdirectories which are sub projects or modules. It gets a bit complicated, but if you have one project you basically need the one file.
settings.gradle
handles project, module and other kinds of names and settings, gradle.properties
configures resusable variables for your gradle files if you like and you feel they would be clearer that way.