Make sure it's really a Buzzer, and not a piezoelectric speaker which are often, incorrectly, referred to as "buzzers" [a buzzer is a device that buzzes when voltage is applied -- a piezo speaker is just that, a speaker, which requires a signal to cause it to make sound].
If it turns out to be a speaker, then using the tone() function will likely cause it to make a sound. Try around 1kHz to 5kHz -- and get ready to plug your ears! If it's too loud, try adding a resistor in series -- something like 100Ω or so -- but experimentation will likely be necessary.
If you have a datasheet for the "buzzer", look up things like resonant frequency, and maximum voltage. Then, set the tone() function to that resonant frequency, and make sure you don't apply a voltage that will exceed it's max [unlikely at 5v 
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