If your a newbie to C2 then this will probably be a hard task for you until you read around or post a thread asking about it.
How To Do It:
Basically what you have to do is use the press of something to simulate control of an object. To do this you can maybe add arrows keys on the screen of your game then add a touch event for "is touch" to the image file. There's other ways to do touch controls but this is for games where all is needed is the touch of buttons to move the player.
If you don't like arrow keys you can create see through png files position it on the screen then simulate a control when it is pressed.
In the picture below i have created two see through png files in Photoshop. Then i put it over my game evenly on both sides when the one on the left is press my player goes left and when the one on the right is pressed my players goes right.
Here is the event sheet for it: