Kotlin Koans are a series of exercises to get you familiar with the Kotlin Syntax. Each exercise is created as a failing unit test and your job is to make it pass. You can play with Koans online or offline by cloning the project on GitHub:
Download the Koans by cloning the project from GitHub
git clone https://github.com/Kotlin/kotlin-koans
Open up the project in IntelliJ IDEA or your favorite editor. Note: If IntelliJ IDEA prompts you to update the Kotlin library, just click yes.
Run a test. Make it pass
Repeat for all tests!
The repository has two branches, master which contains the exercises for you to do and resolutions which contains the resolved exercises. Make sure you don't cheat!