This built on the Express framework, and uses these GOV.UK resources:
Read the project principles.
You may already have it, try:
node --version
Your version needs to be at least v0.10.0.
If you don't have Node, download it here: http://nodejs.org/.
Install Node.js (see requirements)
npm install
This will install folders containing programs described by the package.json file to a folder called node_modules.
node start.js
Go to localhost:3000 in your browser.
This project is built on top of Express, the idea is that it is straightforward to create simple static pages out of the box. However, you're not limited to that - more dynamic sites can be built with more understanding of Express. Here's a good Express tutorial.