Casting On and Live Stitches?

[flutricity]

Hello all, I'm new to knitting and thought I'd try out a small cardigan to practice.
I came across this line in the pattern: Break yarn, CO 10 on right needle, purl across live sts on left needle, CO 10 on right needle.
I'm a bit confused. Am I supposed to end up with 10 new stitches, the middle part, and then 10 new stitches? Should I break the yarn again to cast on the second set of new stitches? Then do I treat it all as one big row when I start the next row?
This is for the yoke of the cardigan, if that helps. Thanks in advance! :D