first you need to know how to script (i use Actionscript 2.0 but you can use something different), and then you need a program to script in (i use Alligator Flash Designer, its really easy and great for beginners as well as people who can do complex scripting)
Making a game isn't an easy thing, you gotta use creativity and have original ideas if you want to make a good, fun game... (the graphics doesn't matter!) Are you sure you want to make games?