There are many commands available to help you build and test sites. Here are a few highlights to get started with.
$ gulp serve
This outputs an IP address you can use to locally test and another that can be used on devices connected to your network.
$ gulp
Build and optimize the current project, ready for deployment. This includes linting as well as image, script, stylesheet and HTML optimization and minification.
$ gulp pagespeed
Runs the deployed (public) version of your site against the PageSpeed Insights API to help you stay on top of where you can improve.