Hello World Flex Application

 <?xml version="1.0" encoding="utf-8"?>
<mx:application layout="absolute" xmlns:mx="http://www.adobe.com/2006/mxml">
<mx:panel height="200" layout="absolute" title="Hello World Application" width="250" x="140" y="42">
<mx:label fontsize="24" fontweight="bold" text="Hello World" x="22" y="28">
</mx:label>
</mx:panel>
</mx:application>

Starting Flex Application

Open Flex Builder 2/3 Click on File -> choose New ->Flex Project select "Flex Project" it prompt a New FlexProject window enter your project name in "Project name" field if you want to a specific location for project "browse" that folder,if not leave as default "Use default Location" in Project location box, select WebApplication in "Application type" at we are not going to add server so that leave as it is "Server tecchnology" box, then click on "Next" leave as bin-debug as output folder then click Next then it show two tabs Sourcepath and Librarypath. default Sourepath is highlihted if wish to Chage file name enter new name in "Main application file" field with extension .mxml ex: index.mxml . click on image to enlarge