The technique is double knitting 2 socks at once, one inside the other. Both sides are being knit there. You can see it panned out with knits and purls here
, forward it to around the 6 minute mark.
The ladder avoidance thing works for everything.
The thing on my finger is a ring I made that is more for regular double knitting where right side faces out on both sides so the strands are always carried together and you can simply pick the strand/color you want off the finger.
But it works to keep the strand from slipping off my middle finger so I'm using it.