CAN-bus + arduino, how is work?

OK, forget the TFT display.

I just want to read the CAN data from the my vehicle (ID) when the position of the hand brake is activated, then the Can-bus shield must be programmed to send a signal to the Arduino input pin at that point and finally to have an Arduino activated external relay via output pin.
That's all.
I do not want to do 47 operations at the same time, only ONE!
Thank you