There are many things that go on in any Flash movie. Learning the flash methods behind them is just a matter of practice and use. There is no easy way or shortcut to learning how to build games with Flash. Games, websites, applications, etc... all rely on the methods available to actionscript and the properties of objects in flash. The real power of Flash is movieclips. Learn how to contain content in movieclips and manipulate the properties of movieclips and you will gain knowledge as you go. The Flash help panel will describe any method in actionscript and give a short code sample on how to use the method. You can download open source projects and see how they were constructed to learn to emulate the code techniques and overall project arrangement. You can do a google search for tutorials on games also. Other than that, it is alot of trial and error. Try to create a simple game and advance your projects as your knowledge of Flash and actionscript increases.
hope it helps
A mind once stretched by a new idea never regains its original dimensions.
- Oliver Wendell Holmes