Make sure the audio service is installed and enabled (file /etc/bluetooth/audio.service should exist)
modify your ~/.asoundrc to contain pcm.bluetooth {
type bluetooth
device 00:11:22:33:44:55
}
where 00:11:22:33:44:55 is the Bluetooth address of your headset (use for example hcitool scan to find it)
configure your audio application to use the alsa device "bluetooth". See Supported Players for some examples.
start playing