What variables to declare for controlling a motor with high power motor controller
Variables are just names assigned to numbers. The names, as far as your program is concerned, are completely meaningless.

It's the numbers you assign to the variables and, more importantly, what you do with those variables that is important.

Your shield seems to have jumpers to select what I/O pins perform which function, so you just need to write the software to control the chosen I/O pins in the right way.