Assuming that you have successfully customised the kernel and your raspberry pi configures the CANbus USB adapter correctly, it's time to test the connection!
Configure the CANbus interface (the number at the end is the baud rate)
sudo ip link set can0 type can bitrate 125000
bring the connection up:
sudo ip link set up can0
Print interface info:
ifconfig ifconfig can0
Set up a listener and send in the background (if you use server version and you have only terminal access)
candump can0 &
and then something to the bus by executing:
cansend can0 123#1122334455667788
To run these tests, you should have installed can-utils package.