JT6m is used mostly on the 6 meter band at 50.230 or 50.260 MHz.  These frequencies are the starting point, usually used after a schedule on one of the internet reflectors.  JT6m however is also used on other bands, especially 17 meters which seems to favor these variable tones and easier to decode.  These YouTube videos explain it better than I can and have to admit is is a lot of fun making contacts on 6 meters whereas otherwise nothing but noise would be heard.  Give it a try and if you use the Flex 5000A, it makes for even better operating since there is no external sound card to insert noise since virtual audio cables and com ports are used.