When I fist placed my order I ordered everything possible including the
3 axis DSP digital stepper driver.
When putting everythig together I noticed this was still left over and that I couldn’t find any instructions for it.
I then forgot about it until I came across it again just the other day.
What is it used for and how do I use it?
this is a type of controller that is used for mainly with Mach3 or linuxcnc they are usually parallel port (printer) not usb. they also allow more axis than GRBL can (think 5 axis with rotary). but are also more complicated to setup to use. but there are some good resources here of people that have done just that.
so it is up to you what type of controller you want and which programs you want to use.