One question each time, ok?
==>Bud how can i Save after a Race in GP3
You can save the season file (if you are in one). If you are in practice, Quick Race or non-chamionship race, there is no sense to save this after the race. So, this option does not exist.
However, maybe you mean to save races results. In this case you have to print the results directing them to a .txt file (in the game, set the option print to file as your printer)
==>How can i drive with my Gamepad ?
Probably your gamepad is recognized by the game as a standard Joystick. So, you have to set (and calibrate) the axis for steering, accelerate and braking into the game. Furthermore, you have to choose buttons for increase and decrease gears and the pit signal.
==>How can i Backward Driving and back normal ?
Well, you have to change the gears down until you reach the Rear Gear. So, you can drive backwards. To drive forwards you have to change the gears up two times (one for Neutral, other for 1st).
==>Gamepad is done, bud when i accelerate my car only turning.
If I have to take my chances, I'll say you need to calibrate your device. But, if you choose to use the X axis for accelerate and the Y axis for steering, probably you are loosing the control of your car.