To start to make Flash Games is actually not that complicated, anyone with a lil bit of passion and time can have a try!
I suggest you to download Adobe Flash CS4 from Adobe, they will give you for free the 30 days trial version, so you can evaluate it.
OnLine you can even find some free programs that compile ActionScript, like FlashDevelop.



Then, when you get your program check on Google for: ActionScritp 3 Tutorials.
You can find the best on the site of Emanuele Feronato.

Kirupa is a good forum where you can register and ask any question you want about ActionScript 3 (Shortly AS3).

On LorenzGames you can have an idea of the best flash games made by the best game designers on the world.
I organized few super best game on another site ILikeToGame, you can check them.

In this industry they pay those games from $3k to $10k for the cool ones or more for awesomeness, or you can just put your own advertising like MochiAds, there are so many ways of monetization with this kind of games, you just need to start and give a try!