You will find that the volume of the noise will be too loud when using headphones. You can change the volume by adding a resistor in series between leg 0 and the headphone tip. Larger resistor values will make the music quieter.

If you want to be able to vary the volume, you can add a potentiometer. Make sure you have followed this activity on using potentiometers. Disconnect your coloured crocclip from your headphones/buzzer and connect it to the power leg of the potentiometer. Now connect another crocclip from the output leg of the potentiometer to the tip of the headphone plug (or free leg of the buzzer). Finally connect the ground leg of the potentiometer to the GND leg on CodeBug.