You can use this template if you want to make your own modules. See this guide for an explanation:
https://github.com/cfengine/build-index/blob/master/CONTRIBUTING.md
This module has a policy file which reports the following string:
Hello from CFEngine Build
The string is printed to the terminal and sent to the reporting hub as inventory information (in CFEngine Enterprise).
It is meant as an example / starting point.
Edit cfbs.json and my_policy.cf to experiment.