you should have gotten an adapter with a usb on one end and the other end plugs into the plug that plugs into your receiver. If that was a little too confusing...unplug the esc from your receiver and plug it into the adapter cable. There is no actual usb on the MMM itself, you have to use the adapter.
Hope that helps, maybe someone else can explain it better if not.
you should only have to program your BEC once, the fist time I programmed a CC BEC I installed before and had issues and I called Castle and I was told to program first but I wonder why when you try to tweak the ESC the confusion doesnt work the other way