What is a motor driver and how would you use it with the Arduino

I got a kit which included a motor driver board. What is a motor driver board and ho would you use it with the Arduino UNO?

You need to give more specific details. What kit? What board?

Also search "Arduino Motor Control" with Google. This is a frequenlty discussed topic.
If you just want to turn the motor on and off, a single power transistor is sufficient. The controller board can supply current in both directions, foward and reverse. Modern boards usually have protection against overloads (overheating) as well as other features.