Dynamic data usually comes from a server. When you are ready to start connecting for Catalyst-designed UI up to a real server, you'll need to import the project into Flash Builder and write some code.
Here are a few tutorials about connecting to a server:
If you instead want the text to be dynamically generated within the application (rather than coming from a server), any general Flex tutorial would be a good place to start -- especially one that touches on data binding. Learn Flex in a week is a good free online video training course.