Step 1: The Parts
a pair of speakers (mine is Logitech USB powered speakers) 15 Euros
a bluetooth headset (mine is a Sony Ericsson HBH-DS200 with a classic headphone jack) ~10 Euros
a bluetooth enabled device and/or smartphone (mine is a Sony Ericsson XPERIA X10 mini)
Step 2: Make the Connections
Then, pair your headset with your device. If you don't know how to do this, then just google your headset's model number and search for its manual. For my headset, turn off the headset and hold down the power button until you see a little circle flash in the screen. Finally, play your favourite music song and hear it coming out to the speakers!!
NOTE: Your device must support outputting music to a headset or else it won't work. But don't worry as most smartphones and iPod touches support it.