Clone the repo. You can then run scripts from the command-line (various gradle tasks have been defined to make this easy) or within your favorite IDE or the Groovy Console.
Details for cloning and showing available gradle tasks:
Linux/MacOS
$ git clone https://github.com/paulk-asert/groovy-constraint-programming.git
...
$ ./gradlew tasks
Windows
Assuming you have git installed:
> git clone https://github.com/paulk-asert/groovy-constraint-programming.git
...
> gradlew tasks
Make sure you have Java installed prior to running the examples.
Alternatively, run any of the scripts directly in the IDE.