Online documentation

You'll want to be sure to point your browser to the online documentation for Node and bookmark it, as it will undoubtedly become a resource that you will want to access on a regular basis. It is not mandatory that you should go through each and every section of it, but once you start writing code in Node.js, you will need to refer to this document frequently to understand more on the APIs exposed by Node.js. The document is available at http://nodejs.org/api/.

Also, check out the npm registry available at http://npmjs.com, where you can find tens of thousands of modules available for Node developers.