Gradle utilizes a logging framework. You can log messages to that. By default, only log level lifecycle and above are shown, but you can log at other levels such as debug and info.
To log at debug level (visible with builds using gradle --debug or lower)
project.logger.debug('my debug message')
To log at info level (visible with gradle --info builds and lower)
project.logger.info('my info message')
To log at lifecycle level (visible by default)
project.logger.lifecycle('my message visible by default')