If you are looking at this from IntelliJ IDEA you can start by expanding the _project_ tab on the left. You will find a template program in `src/main/kotlin/TemplateProgram.kt`
You will find some [basic instructions](https://guide.openrndr.org/#/02_Getting_Started_with_OPENRNDR/C00_SetupYourFirstProgram) in the [OPENRNDR guide](https://guide.openrndr.org)
To create runnable jars for a platform different from the platform you use to build one uses `./gradlew jar --PtargetPlatform=<platform>`. The supported platforms are `windows`, `macos`, `linux-x64` and `linux-arm64`. Note that the `linux-arm64` platform will only work with OPENRNDR snapshot builds from master and OPENRNDR 0.3.39 (a future version).