Welcome to the Liferay's Developers Guide, the official guide for all developers that want to develop a portal based on Liferay or that want to develop an application that anyone can use in their Liferay installation. This guide will asume that you already know what a portal is and know how to use Liferay from an end user perspective. If you don't, it is recommended that you read the What is a Portal? Whitepaper and chapters 1, 5 and 6 of Liferay's Administration Guide.
This first chapter introduces the technologies and tools that you will be able to use to develop applications and also to extend or customise the functionalities that Liferay provides out of the box to adapt them to your needs.
The main mechanism that you as a developer will use to achieve all of the above in a modular way are Liferay Plugins. Liferay Plugins are always distributed as Web Archives (.war files), and deployed through Liferay's deploy mechanisms. There are different types of plugins depending of its purpose. The following sections describe how to develop applications for Liferay and how to perform customizations and the types of plugins that you can use in each case.