I have learnt most action script and would like to make a game. I have have good idea but the only problem is that I do not know where to start. If anyone could help me I would be very grateful.
you shouldn't asking that if you learnt 'most action script'. you choose a framework to work with (box2d, lassie etc) or you start your own game engine and that's it.
yes. decent games are based on a game engine, unless you are talking for something really primitive like a match the colors or space invaders. have a look here http://en.wikipedia.org/wiki/Game_engine