Gradle is downloadable as a zip file at http://www.gradle.org/downloads. Only the binaries are required, so look for the link to gradle-version-bin.zip. (You can also choose gradle-version-all.zip to get the sources and documentation as well as the binaries.)
Unzip the file to your computer, and add the bin folder to your path.
run Gradle from the command-line:
gradle build
or
gradle war