Below are the list of important resources which would help you getting started with Aparche Flex 4.8.0
Announcement: Release of Apache Flex 4.8.0
Apache Flex Installer
http://flex.apache.org/installer.html - The Apache Flex SDK Installer simplifies the download and installation of the latest Apache Flex SDK and its components onto your computer for anyone who might not be familiar with compiling from source code but wants to use the latest release of the Apache Flex SDK and prepares your favorite IDE such as Adobe Flash Builder or JetBrains IntelliJ IDEA by downloading its binary distribution from apache.org or its mirrors, and install it .