Maybe you could do what I do:
Start with an example program that doesn't even do what you want on your final project (maybe just says 'hello' on the serial port). Don't worry yet that it isn't even close to being your completed project.
As you see the example work, try changing something on the program. Soon the changes will help you make other changes toward your actual project. It begins to form into your project, and eventually you will have the project working.
The hardest thing for me was to get started because I was trying to have the whole thing figured out before I started.
Also if you look in the MCU docs and can't find or can't understand a specific section for some feature, that's a good thing to look here for answers. Specific means for example, "I looked in S12CRGV2.pdf and can't find where it says what clock the SCI uses".
Good luck, we all need a little of that too