[puppet] How to print something when running Puppet client?

Just as alternative you may consider using execs... (I wouldn't recommend it though)

exec { 'this will output stuff':
  path      => '/bin',
  command   => 'echo Hello World!',
  logoutput => true,
}

So when you run puppet you should find some output like so:

notice: /Stage[main]//Exec[this will output stuff]/returns: Hello World!
notice: /Stage[main]//Exec[this will output stuff]/returns: executed successfully
notice: Finished catalog run in 0.08 seconds

The first line being logged output.