The first number (3) means how many "flat" channels there are, in this case, a left channel, right channel, and center channel. The second number (1) means how many dedicated subwoofer units there are, in your case, you there is 1 wireless subwoofer included. The third (2) number means how many upwards firing channels there are, in this case, there are 2 upwards firing drivers built into that soundbar that is meant to simulate ceiling speakers.
(this applies to all surround sound setups)
Hope this helps.