Australia, and a few lucky countries, use 1-13 in the 2.4Ghz band.
USA, and much of Europe/the rest of the world, use channels 1-11 only.
Non overlapping/interfering channels are 1, 6 and 11 or 1, 7 & 13 for lucky countries.
Each of the above channels are 20MHZ (54 or 150Mb/s). When using 40Mhz (108Mb/s or 300Mb/s mode) your wifi network will use 1+6 or 13+6, meaning that there will be some interference in communications on the mid channel (6/7).
If you have a 5Ghz wifi network and a 2.4Ghz network, this is excellent
I personally have a 2.4Ghz 802.11G on 13 (other end of house), 802.11n (300) on channels 1&7, and a 5Ghz 802.11n (other end of house) ....