OK, so you want to make some noise and are not going to be able to lay your hands on a suitable 3V buzzer. Don't worry, you can play some noise through your headphones if you use some alligator/crocodile clips.
In the photograph, two cables are attached to jack on my headphones,
The black lead is connected to GND on the micro:bit, the red lead is connected to pin 0.
The base of the headphone jack is GND. The tip of the jack is one ear of the headphones.
Do not put the headphones in your ears when you test this. The sound will be pretty loud. If you don't get any noise, and you are sure that the program is correct, check that you have the crocodile clips in the correct place and they are not sliding all over the jack. It's a bit of a delicate setup but it will let you hear your micro:bit sing.
If you need to calm the noise down a little, you want to see if you can squeeze a resistor into the circuit. I managed to hold a 470Ohm resistor in one of the crocodile clips, the one attached to the tip, although it should not matter. This reduced the volume a little but still made plenty of noise. The tone through the headphones sounds a little nicer to me than the PCB buzzers I normally use. I am old, though, and my hearing is not particularly sensitive when it comes to sound and music.