You can find SDKs, as well as sample apps, technical documentation, and FAQs for them, at https://developer.samsung.com/home.do. Click here to find a list of SDKs, and click each SDK to find its download, samples, and other useful documentation.
You can use the Tizen platform to create Samsung Galaxy Watch faces and apps. See tizen.org for samples and other documentation, such as the following:
- Gear native samples: https://developer.tizen.org/development/sample/native
- Gear web samples: https://developer.tizen.org/development/sample/web
- .Net samples: https://developer.tizen.org/development/sample/.net-application/account
- Companion samples: https://developer.samsung.com/galaxy-watch/develop/samples/companion
- More samples: https://developer.samsung.com/galaxy-watch/develop/samples/more