yep its done when you want to hold extra queens that you don't want to use yet, I'm no expert but if you take a frame without foundation
and put a peice of wood about halfway , going hoizontal
you put the queen cages between the top bar or the bottom bar and the
new peice of wood. there are many differant ways to bank queens
what i did was , I made sure that the queen was in the bottom brood box,
then I put the queen excluder on, then the top brood box , then I put the frame with the queens in the top box.
you just have to make sure that the queen thats in the bottom can't get to the queens in the top box. or she will kill them!
the workers will feed them.
I've had three banked for 2 1/2 weeks or more , just ckecked today .
they are all in good shape!
another way is to make a queenless nuc then put the frame set up in it.