> For the complete documentation index, see [llms.txt](https://docs.january.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.january.ai/client-sdks/react-native-sdk/concepts.md).

# Core concepts

* [Client lifecycle](/client-sdks/react-native-sdk/concepts/client-lifecycle.md): one client per signed-in user, created and disposed with the session.
* [User identity and timezone](/client-sdks/react-native-sdk/concepts/user-identity-and-timezone.md): what `endUserId` does, and which calendar days list calls cover.
* [Food details and portions](/client-sdks/react-native-sdk/concepts/food-hydration-and-portions.md): turn a search result into a food, serving, and quantity you can log.