Ensure you have an updated version of nodejs and npm installed. Ubuntu repos often contain an old version, so it's recommend to use a more up-to-date repo.
If you already had nodejs installed and need it updated, make sure to sudo apt-get update && sudo apt-get upgrade. Otherwise a sudo apt-get install nodejs npm should be sufficient.
brew install node
Install node from http://nodejs.org/download/ and open the node command prompt.
Assuming nodejs/npm is correctly installed, the next step is to install gulp with sudo npm -g install gulp.
npm install && gulp build
This will install all dependencies and compile the site to ./build/ (or whatever is defined as basePaths.dest in gulpfile.js). To instruct gulp to compile for production, pass --prod and possibly gulp bundle to compress it into a zip. For example:
gulp build --prod && gulp bundle
Or use the default dev task, which launches a local live-reload server for preview:
gulp