You'll need to have Node.js installed for this.

Windows

If you're on Windows, I recommend installing it via https://nodejs.org/en/

Mac

Otherwise, if you're on Mac I recommend using Homebrew: https://brew.sh

You can then run:

# Add Homebrew to your PATH
$ export PATH="/usr/local/bin:$PATH"
# Install Node
$ brew install node

In both cases you should then be able to run:

$ npm -v
$ node -v

If you get two version numbers back, this means you have Node.js correctly installed.