Newbie to can and obd2

Hello every one
Im newbie to can bus and obd2 system, for my project digital instrument cluster using rp4 with 12.3 screen, but my problem is I need some one to explain how to generate obd2 messages and send them to real dash, and creating xml file, i download the example file but i didnt find it useful without knowing how it works, and for the sketch using mcp 2515, not working at all

Your question is very broad and difficult to answer in couple of sentences. Typically its your car that generates those messages and then RealDash interprets them based on a instructions from XML file.

See documentation for OBD2 XML:

RealDash-extras/OBD2/README.md at master · janimm/RealDash-extras (github.com)

And for CAN XML:

RealDash-extras/RealDash-CAN/realdash-can-description-file.md at master · janimm/RealDash-extras (github.com)

I read this, but because im newbie to obd and can, i fail to that, the example sketch is very noisy and has many lines, if you can write simple sketch for one value like fuel level only , and its xml data.
I would appreciate that.
In This way i will start creating and learning

I hope you don’t get offended, but if our Arduino example seems too complicated you will need some help to get started.

Try to find a local friend of colleague that can sit with you for couple of hours to explain the basics of Arduino programming.

Also, maybe you could explain in more detail about what you are trying to achieve? There is a good chance that there is already a solution for your problem that you can just install and start using in your project.