The easiest way to install the smart mirror is via the 1-line installation script for the Pi (or other systems) This script will install the smart mirror and it's dependencies:
curl -sL https://raw.githubusercontent.com/evancohen/smart-mirror/master/scripts/pi-install.sh | bash
Using another platform? Something went wrong with the install? Want to do things the old fashioned way?
That's OK. That's why there are manual installation instructions: