Need help on a Debbie Bliss pattern!

I am sure the answer will be relatively simple - but I am stuck before I even got started. I am wanting to make a child’s zebra scarf from the Debbie Bliss Fall/Winter 2009 magazine.
The pattern reads: 2nd and 3rd rows Cast on 3 sts, k to end. 4th and 5th rows Cast on 2 sts, k to end.
My question is - how do I “cast on” additional stitches after I already have a row knitted? I know how to increase, but this confuses me! Any help? Thanks in advance!

Use a knit or cable caston. Put the needle with the sts in the left hand, cast on, then knit the sts.