The action button is located on the right hand side of the headphone, below the USB charging port.
When you press and hold the action button, when the headphone is on, the headphone will go into pairing mode to connect to a new Bluetooth device.
When pressed for a short click, the action button does the following:
1 click: Play/pause (answer/end calls using audio cable)
2 clicks: skip track forward
3 clicks: skip track backward