A:

Just like you'd play a 2D one, except that to give the sound a position in 3D space, you'll need to pass its location to AIL_set_sample_3D_position. Unless your sound positions are relative to a listener at the origin, you'll also want to pass the listener's location to AIL_set_listener_3D_position.

Note that 3D audio data should be mono (not stereo) under most circumstances. See the "How can I assign 3D positions to stereo samples?" FAQ for more details.

Most likely, your application will also need to use the AIL_set_sample_3D_distances function to set the 3D volume-falloff characteristics. See the "My 3D sound isn't falling off like I expected..." FAQ for more details on 3D distances.