I'm new to Svelte and three.js, where should I start?
For questions regarding Svelte or three.js usage / APIs please visit their official websites:
Svelthree aims to offer an API close to the one of three.js for Svelte-developers, so it seems more logical to start with Svelte. A certain amount of experience with both Svelte and three.js would be best.
Where can I find the API documentation?
Svelthree is still in an early "proof of concept" development phase and many cool features are yet to be added, so the API may change in future releases while always aiming to provide a rich feature stack along with the best possible developer experience.
Nevertheless the "current state" API documentation is in the works and coming soon. Meanwhile you can explore the Examples section where new content will be added constantly in order to cover the API in detail.