You'll need to have Node.js installed for this.
If you're on Windows, I recommend installing it via https://nodejs.org/en/
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.