You apply 5v DC across a buzzer (this is a polarised device like a diode, it only works one way), and it emits a (fixed frequency) tone.
Rated at 5v nominal, they actually seem happy to beep even off a 3v coin cell, just quieter/different frequency is all.
Approx 12mm wide, 10mm high, they come with a sticker covering the sound hole to stop stuff getting in it, remove that before use )
Note, this is not a "speaker", it's an active beeper, it emits just one tone, beeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeep, you can't make it play different notes.
Not much more to say, if you need an alert beep for your project, this is the easiest way.
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