Nodemailer is basically a module that gives you the ability to easily send emails when programming in Node.js. There are some great examples of how to use the Nodemailer module at http://www.nodemailer.com/. The full instructions about how to install and use the basic functionality of Nodemailer is included in this link.
I personally had trouble installing Nodemailer using npm, so I just downloaded the source. There are instructions for both the npm install and downloading the source.
This is a very simple module to use and I would recommend it to anyone wanting to send emails using Node.js. Good luck!