First, make sure you have the Polymer CLI installed. Then run polymer serve to serve your application locally.
$ polymer serve
$ polymer build
This will create builds of your application in the build/ directory, optimized to be served in production. You can then serve the built versions by giving polymer serve a folder to serve from:
$ polymer serve build/default
$ polymer test
Your application is already set up to be tested via web-component-tester. Run polymer test to run your application's test suite locally. Java SE Development Kit 8 is required. Note that if you do not have the javac command installed, you will be promted to install Java 10. To uninstall Java, see the direction here. See issue #405 for the status of Java 10 support.