First of all you need Node.js to get started. If you don't have it already you can download it here
Once Node.js is installed, open Terminal and run "npm install" to install all of GO dependencies. New folder
node_modules will be created automaticaly.
Now you're ready to start building new pages. All you have to do is run "gulp" in Terminal. This will track all the sass file changes and start a local webserver at http://localhost:3000