Cast on stitches in the middle of a work

So I’m working on the attached pattern for a doggie sweater. The part that is troubling me is the arm holes. I was able to bind off to make the holes, but now I don’t know how to cast back on the 6 stitches I need for each side. I’ve only ever done a long tail cast on. Any suggestions on which method I should use? I tried watching the videos in the cast on section of the site but I just got really really confused.

Use the knit or cable cast on. You don’t have to start with a slip st, just pretend you’ve already cast on a bunch of sts. Move the needle with the sts on it to your left hand, and knit into the first one (or between the first 2 sts), don’t take the st off the left needle, put the new st on the left one and repeat. When you’ve added 6 sts, move the needle back to your right hand and knit the next section.