Looking for a tutorial on adding node.js (& npm) tomy server

A quick answer is to follow Nodesource's instructions to install Node.js and npm for Debian here: https://github.com/nodesource/distributions#debinstall

You can confirm installation and versions of each with these commands:

node -v
npm -v

Otherwise, you can find extensive documentation directly from npm here: https://docs.npmjs.com/