If you are using Flash Builder you may want to do some of the getting started tutorials and also look at Tour de Flex from Adobe. Those things really helped me a lot. The tutorials are good for learning the basics, but you probably won't want to do all of them since they are very long. Tour de Flex helped me to learn about the different components and objects, how to use them, and what they do. You may also want to pay attention to the code hints as you write your app in Flash Builder. They helped me overcome several problems.
As for the signing I can't help there since I am still having problems with it too, but since you are just starting on your app, what are you trying to package and sign? Even if you are succesful in signing now you will still have to sign again when you are done with your app.
