If you don't have a developer account yet, get one for free. You need an account to use the SDK.
You also need to register an OAuth 2.0 app via the form on circuit.github.io.
The entry point for the SDK documentation is the module Circuit with its main class Client.
Node.jsNode.js example apps are on github. E.g.
- webrtc-bot-example (electron app)
Runkit allows playing with Node.js modules live, similar to jsbin or jsfiddle on the client. Try it on runkit
See README on github.com/circuit/circuit-sdk for more info.