first you must learn how to make games the program will not teach you that take a course at a collage or something plus the system costs a few hundred dollars making games is not easy learn how first
There are several game making websites (e.g. Sploder). However I would suggest trying Game Maker, its a downloadable program which allows users to develop -rather easily- computer games, without requiring any programing experience. Plus its free.
If you want to buy flash I suggest buying the Education Product. Adobe Flash Professional CS5 Student and Teacher Edition costs 179 $, you are required to submit proof of eligibility prior to shipment though.
Adobe games are the only games you can upload to the site, but it's EXPENSIVE!!! There is a program called game maker that I took a 5 day course on once. You don't need script to make these games, and the lite version is free.