yeah you need adobe flash for it. the scripting language of flash is called action script. so you need to know how to use adobe flash and how to write scripts in action script.
I think I've made.... lets see...... 9 games, 5 full games using Game Maker 8. I love it. If anyone wants to create a flash game, go for Game Maker. Not to mention that there's infinite possibilities. My favorite part is the built in sprite creator.