i want to learn game developing process, how can i learn it easily?

It can't be learnt easily, best to accept that now. Do you already program? If not, your first course of action should be to learn C. Once you more or less understand C, start downloading source code for a simple game, read through it over and over until you begin to understand what's going on.

Also accept that it's going to be years until you can produce something that looks like the games that inspired you to do this. Then, start with the basics, like C (and, since you're on this particular forum, Objective-C). Write small programs that aren't games first, so you can learn how to read files, how to process text and images, how to make a working GUI, and other basic tasks. Then move on to cloning very simple pre-existing game designs like Hunt the Wumpus or Pong.

I'll third what NelsonMandella and Mark Levin said: there isn't such a thing as easily learning game development.

There are basically three ways:
1) learn C
2) go for a scripting language/game environment which might make your life easier, like Python/PyGame or some modern derivative of BASIC
3) find a game engine, like http://unity3d.com

None of them are easy, although options 2 or 3 are arguably *easier* than option 1. If it were I who was starting out and I wanted to do 3D games, I'd do Unity3D.