Kotlin can be written using any plain text editor. However, we recommend using IntelliJ, especially as you are learning. Just as text editing software that offers spell check and grammar check makes writing a well-formed prose essay easier, IntelliJ makes writing well-formed Kotlin easier. IntelliJ helps you:
write syntactically and semantically correct code with features like syntax highlighting, context-sensitive suggestions, and automatic code completion
run and debug your code with features like debug breakpoints and real-time code stepping when your application is running
restructure existing code with refactoring shortcuts (like rename and extract constant) and code formatting to clean up indentation and spacing
Also, since Kotlin was created by JetBrains, the integration between IntelliJ and Kotlin is carefully designed – often leading to a delightful editing experience. As an added bonus, IntelliJ is the basis of Android Studio, so shortcuts and tools you learn here will translate to using Android Studio, if that is your thing.