Stepper drivers require a pulse for each increment of travel. For example if steppers set for .01 mm per pulse then you need to send 100 pulses to move stepper 1mm.
This means you have to calculate every point on the path to the resolution of your cnc drives. You then have to send pulse to each axis at the same time to move all axis to the required result.
For example at .01mm resolution to move in a straight line 1 mm in X and 2 mm in Y you would send pulse to Y only then a pulse to X and Y to move X .01 mm and Y .02mm you would repeat this 100 times to move X 1mm Y 2mm.
On top of this you need to time the pulses to have motors run at the desired speed.