This document provides an overview of uploading files in Flex using the FileReference class. It discusses the basic steps, which are to display a dialog box for the user to select a file, upload the file to the server, process it on the server, and return any necessary data. It then describes the FileReference class and its properties and methods for browsing, selecting, uploading, and canceling a file upload. Events that can be used during the upload process are also covered, along with the FileFilter class for restricting file types.