I wonder if there is some serious confusion here seeing as the OP is a beginner.
For Arduino projects the word "servo" usually means the sort of thing that is used to move the control surfaces of model aircraft. It's often referred to as a hobby servo or an R/C servo - but mostly just as a "servo".
In the industrial machining world the word servo is also used to refer to a sophisticated and expensive device that can be used in place of a stepper motor - I would be surprised if that is what the OP has in mind.
Conceptually a hobby servo is very different from a stepper motor. Servo's are designed to move to an angle between 0 and about 180 degrees in response to a command from the Arduino. Stepper motors, on the other hand just move one step at a time very accurately (and are not restricted to 180 deg) but there is no way to tell what angle they are actually at.
There are many applications where either a servo or a stepper could be used. In general servos are cheaper and much easier to use if they are suitable for the application.
...R