Since Kotlin can be compiled/transpiled to many languages, we want to say hello world using different runtimes (JVM, Node, native == your OS).
There is the shared module commonMain which defines a Greeter class which is used on every platform. It defines a function getPlatformSpecificMessagePart marked with the expect keyword. This means that it expects each platform-specific module to implement this function in its own way.
Go to each of the three submodules. Adapt the implementation of getPlatformSpecificMessagePart by using platform-specific Kotlin.
The solution will always be a short one-liner. Since we have only introduced very few concepts in Kotlin yet, try not to question every line in this module.
Start the associated application to verify the result.