Well, you need to get Adobe Flash and then learn ActionScript 3.0. ActionScript is the scripting language used in all flash games, and 3.0 is the latest version.
I suggest you first get the trial from Adobe's website, here's a link, and then have look around.
When I started off, I found that books is the best way to learn AS3. Because you want to get into games, the best choice will be first to get a grasp of ActionScript 3 basics in Learning ActionScript 3.0: A Beginners's Guide. When learning always make sure that you put the code you learned into practice in Flash. By the time you finish Chapter 6, you can move on to Flash Game University. It's an amazingly good book and I learned the main foundations opf game programming from this book. First it talks about basic game features like moving with arrow keys, movement of characters on the screen(animation) in 3 different ways, visual elements etc. Then you learn various concepts by making example games. It's a really good book.
Remember not to get discouraged as I did. Always try to experiment with your own ideas and if they don't work, try to figure out why. Making games is very fun, but it's not effortless. If there's something not in the books, look up an online tutorial for it(don't rely on them too much though). Once you are sure you want to go into this and can do a relavitely good amount of things, get this book: Essential ActionScript 3.0; it really is a must for any good flash developer, it is very in-depth and detailed about many of AS3.0 concepts.
I hope you have fun learning to make games, you can email me if you want to ask some more question: manny6574@hotmail.co.uk
Have Fun! ;)