DN and SN is basically Deep National (brood Box) and Shallow National (super).
1,2 etc are just different types of frame. DN/SN1s are basically your bog standard frame, you need spacers of some description with these. DN/SN2s are basically the same but I believe with a wider top bar. DN/SN3s do these actually exist? I guess they must do, no idea what they are off the top of my head.
DN4/SN4s are Hoffman "self spacing" frames. Tend to be more common in brood boxes although I somehow ended up with a batch for the supers, they soon ended up with spacers on them anyway so not much advantage in the supers and pointless if you use castellated spacers.