The PlayStation 3's DualShock 3 controller wasn't originally designed with the PC in mind. But who cares: We're gonna do it anyway. The DualShock 3 isn't quite as easy to use on PC as a modern Xbox ...
Press and hold the PS and Share buttons on your DualShock 4 until it enters pairing mode (shown by the flashing white light bar on the back of the controller). Open your Android phone's Settings app.