Arduino: Control VW Golf 4 Speedometer

Hello,

I'm new to this forum and would like to introduce myself briefly.
My name is Alexander, I'm 24 years old, and I'm relatively new to the world of CAN bus and Arduino.
I drive a Volkswagen Passat 3BG 2.5 TDI and also a Volkswagen Golf 2 F&I GTI.
This forum was recommended to me by a colleague who frequently reads it and almost always finds solutions through it.

Okay,
Now, to my problem.
I want to use an Arduino Mini Pro and a MCP2515 CAN converter to access data such as engine speed and airbag warning light status.
"Where's the best place to start? I don't have any issues with hardware; I have plenty of tachometers available, and other parts as well."
I've already set up the test environment, and I can send data via the CAN bus, but it's not responding. It's probably just that the signals aren't correct.