A servo motor will rotate to an exact position, based on what it is being commanded to do. An example is the steering on a radio controlled car, where a servo is used to move the front wheels ‘to’ an exact angle
A stepper motor will move forward or backward one step, each time it is told to move. It will move as quickly as it is ‘stepped’ by its driver circuit.
The main difference is that you tell a servo where to be, but you tell a stepper motor how far to turn.
Generally, a servo motor can only turn about 180 degrees, whilst a stepper motor can keep turning as many rotations as you tell it to, but you need to work out where it is.
So, on a model robot car, you could use a servo to steer the front wheels, and a stepper to drive the rear wheels.
Stepper motors are driven by turning coils on and off internal in the correct sequence (stepper motor drivers simplify this), whilst servo motors accept a pulse, and the width of the pulse tells the servo where to be