How do you get into programming marlin2 firmware?

Im wondering how I get into marlin2 firmware development? I’m currently trying to use an SKR V1.3 to control several stepper motors but I need them to do asynchronous things simultaneously(like having 1 stepper motor control lidar system movement and 2 stepper motors controlling wheel movement).

However, changing what stepper motors are doing or the lidar system is doing using g-code requires interrupting what every stepper is doing so I was hoping to look into how the stepper drivers are sent instructions by marlin2 and bypass using g-code so I can simply send move instructions directly to the stepper drivers.

I want to figure out where in the firmware marlin2 sends instructions to control my particular board’s stepper drivers so I can hijack it, but im not sure how to jump into the firmware since I couldn’t find any tutorials on marlin2 development so im asking here. How do you get into programming marlin2 firmware?