From FDT Documentation
Basic AS3 Tutorial.
Beginning with FDT4, creating AS3 projects has never been easier. FDT 4 now features powerful template management that are designed to help developers get up and running in a flash.
If you haven't installed and created your workspace yet, check out the Installing and Running FDT tutorial to guide you through the process.
Once you have FDT open, you have a few different ways of creating a new project. You can click "Create new Flash Project" via the Welcome Screen