Well it really depends on which version of Flash you are using. Most likely you are using the latest version (8) and therefore will be utilizing Action Script 2.0 (AS2)
The best way to start, honestly, is to build a game. Particullarly Pong.
You can find many tutorials online. The KEY though is to actually type the codes and make the animations. Don't just copy and paste the AS code and download the tutorial authors art.
You will need to start learning tweens, motion and shape. Then variables, text box differences, nesting Movie Clips, etc etc. As you go you will learn a little bit at a time. It is a daunting task, but a fun one as well.
Of course everyone learns differently, but you will find your niche. Start by learning the interfaces of the program.
Then check out the tutorials that came with Flash. Then go here:
http://www.flashkit.com/tutorials/
There are thousands of tutorials here, from physics calculations, like gravity and rbounding, to complete games, to AS, and even a newbie section.
Great rescource!
Good Luck!