A buzzer is generally a low power device, around 20-30mA, and can often be driven directly from most outputs.
Some devices may need a transistor driver, a single transistor type should be adequate.
Remember to observe the polarity.
Use an NPN Transistor Driver - remember that the driver sinks current - so connect between +v and the output of the transistor.
The buzzer will sound when the "Input" goes low (to 0v))