dual channel works in combination of 2 sticks, i.e 2sticks run dual channel and 2x 2stick run dualchannel
quad channel works in 4 stick combination, i.e 4 sticks at a time
the difference is its specified by you motherboard/CPU what configuration is supported
if you motherboard has 4 RAM slots, you can put 4 sticks in and it would run in duall channel if your CPU supported it, or quad channel if your CPU supported that
quad channel is "theoretically" tiny bit faster/better, actual performance difference there is almost 0 from dual/quad channel,
however if you CPU supports dualchannel, using only 2 sticks will perform a tiny bit better than using 4 sticks in DualChannel(2x2sticks in dualchannel)
so find out what your motherboard/CPU...