Well those plugins are source only, so you have to pull them and build them. From there, you copy the artifact to the deploy dir of your Liferay install and it will take care of the rest.
We don't normally contribute there, they showcase basic 'hello world' type portlets in different frameworks to help get your team up and running w/ what they're familiar with, and/or they highlight other Liferay technologies.
When folks want to contribute plugins, they usually use the marketplace to do so. They accept free plugins, even w/ source, so you can distribute what you want for the world to see...
