Missing link

Hello, I am new to this group as of today. The archive here is huge
and having trouble searching through it all, but will continue to do
so. My question is: I am wanting to build a 3 axis gantry machine such
as the Torchmate. It will run plasma and a wood router. The mechanical
part is something I can figure out, but the electronic is something
still a bit confusing. I know you have a Computer running some CAM
software, a power supply, some drive controllers such as "Gecko" and
some Stepper motors. Does the computer send a signal to the gecko
directly, or is there another piece that I am missing? I am wondering
exactly what part of a CNC system does the computer hook to and
communicate with. And also will a gecko provide feed back to the
computer to keep track of what step it's at to keep from losing
position? Thanks.