If you are totally confused by the description of Node.js on their very own website, you are not alone.
To bring back your sanity, first of all, you need to unlearn Node.js:.
2. Node.js has nothing to do with web servers, HTTP, web pages, web applications.
So what exactly is Node.js?
Node.js is a console application very much like PowerShell, with its own scripting language and objects. Basically, you write scripts and run it in Node.js to do some tasks.
It is best used for writing servers because the library of server objects provided and the language itself has a unique concurrency and event call-back I/O model that handles asynchronous operations.