This is the most simple thing ever:
you cast onto one needle. then work it off with the second needle. Then you turn your work and work off with the empty needle again.
you always work off the end that the yarn is on (just like you do with regular needles)
Just never join anything, of course. The stitches can remain on the needle-part (with smaller pieces) or ride onto the cable. You can fit a LOT of stitches onto it.
I do straight knitting with circulars exclusively. I do not own other needles (except double pointed of course). It is a lot more ergonomic since you work with a smaller motion (needles have less leverage since they are shorter)... and instead of holding the knitting up or having it pull down on the needle it will fall into your lap / drape down closer to the needle tip and pull less.
Enjoy your new way of knitting