If you import the module in a project, you see you need to input a string on the publishing side, and you get that string on the receiving side.
To send useful information, you usually have a object structure on the publishing side and you use an export mapping to create a JSON string. You publish this JSON string. On the receiving side, you now have a JSON string and you use an import mapping to transform that string into an object structure. You can then use that object structure normally.
Export and Import mappings are explained in this learning path.
This is all on the Mendix side, however. To get this to work, you also need a Kafka service. You can set one up yourself, or use a fully managed on, like e.g. Amazon MSK
Do you have a runing kafka environment? If yes you could create a test project, implement zhe module and start testing the module. If you have a specific question,you could create a forum entry.
Have you checked the documentation on the app module page in the app store? There are the information you should require for set up the producer and consumer.