Once a project is created, you should have the following directory structure:
You just type ant to build your project. Once the build is finished. You will have an xar file under the build directory. You can then deploy the application to your XPE server.
Under the src directory, there is an xar directory. Then there is a META-INF directory found under the xar directory. There are three important files here: urlPattern.xml, xar.xml and xpipedef.xml.
The directory hosts XSLT scripts and other XML documents needed for the application. By convention, XML documents are stored under the content directory while XSLT scripts are stored under the xslt directory.