Liferay is impressive. Extending and creating applications (portlets and integrations) is merely a piece of cake. Here’s the basic of all basic portlet development using Liferay. Portlet Framework
Basically, this is almost the same way of creating any generic portlet (portlet that complies with JSR – 168 / 268). It just forces you to use its underlying framework.
More Portlet Basic Tutorial (Database Transaction Tutorial)