The easiest way to start a motion path for a camera with C is to take your camera and put it at the starting position. Then move your timeline slider to the end position and a new keyframe will be created. THEN change the motion type to motion path. Say yes to the dialog box to accept the change and you will see a motion path appear that will follow between those 2 points. Now you can add points and move them and all that fun jazz. Have fun! :D