Custom Configuration procedure

Hi everyone ,
I am planning to implement the custom configuration on my vehicle however I am facing confusion while understanding the steps from the link given below:
https://www.ardusub.com/developers/developers.html#making-a-custom-configuration
I have read the link multiple times, gone through other BR forum topics also, yet I am confused from where to start.
I have installed WSL, Ubuntu , then Git.
Please can anyone guide me in steps like from where to start and how to upload the config file smoothly.