# Custom Commands and Functions

* You can define your own [commands](https://docs.yarnspinner.dev/yarn-spinner-for-other-engines/bevy/creating-commands-functions/creating-commands), which allow the scripts you write in Yarn Spinner to control parts of the game that you've built.
* [Functions](https://docs.yarnspinner.dev/yarn-spinner-for-other-engines/bevy/creating-commands-functions/creating-functions) are units of code that Yarn scripts can call to receive a value. In addition to the [built-in functions](https://docs.yarnspinner.dev/write-yarn-scripts/scripting-fundamentals/functions#built-in-functions) that come with Yarn Spinner, you can create your own.