For those that are new to CNC and don't really understand all the terms and what it takes to bring an idea from thaught to making the machine do it's thing.
Not too long ago I fell into that catagory and still do to a certain point (I think I have it figured out)
So let me give it a go...
Cad is the design software that is used to create the part.
Cam is the program that is used to create the machine code (Gcode).
Then you have the controller program that reads the Gcode and makes the machine run.
On things like cutting a picture into a part you can skip the Cad and import it direct into the Cam (if the cam supports this).