stepper motor digital frequency and speed?
You have to look at the datasheet of the stepper.  There is usually a maximum step rate, and sometimes maximum acceleration/deceleration requirements.  Those of course vary with load drag and inertia too.

When working properly, a stepper moves exactly as driven.  You sequence through 10 steps and the shaft should rotate the angle for 10 steps.  However, this is generally open loop, so there are constraints within which you have to operate if you want to be assured the stepper really did what you commanded it to do.

The faster you sequence through the steps the faster the motor turns, until it looses lock and then it will usually just sit there and vibrate.