Its like this:

Now, should I be going out of the jack all the way to the left of the speaker output section there? And then should go out of the unused jack on the back of the first cabinet into either of the two jacks on the back of the second cab?
Should I use the middle jack on the speaker output section of the head? Should I go from one of the two 8Ohm output into one cab and then out of the other 8Ohm output directly to the second cab?
How exactly should I do this. I just got the new cab today and don't want to dollywaggle anything up. This is my first experience hooking up a double 412 rig. Its rather pathetic but I'd rather be safe than sorry.
I apologize for what must be a no-brainer but the fact that the first two outputs are double labeled as "1 x 8" AND "2 x 16" at the same time is simply derailing my confidence in understanding what I'm doing.