If you think about it--a circ is just a long flexible DPN!
if you've never used 2 circs--just cast on.
mark the mid point.
Join into round, knit to mid point. pick up second needle, continue round with second needle
Knitting on 2 circ's feels like flat knitting --you knit all the stitches (from tip A of needle1 to tip b of needle 1.
you turn the work (like flat knitting!) and knit all the stitches on Needle 2--working from tip of needle 2 to tip B of needle 2.
it helps if you have slightly different needles (different colors if metal--or perhaps different lengths.)
Its my favorite way to knit in the round these days.