Baby Kimono Knitting Question?

I am new to the knitting realm and need help with a pattern.
After 4" of garter, the pattern says “using thumb or backward loop cast on 3 stitches at the begin of next rows”. My main question is how do I cast on 3 additional st to the existing work?

It’s also known as a backward loop cast on.
http://www.knittinghelp.com/videos/cast-on

It’s called the loop cast on here, but it’s the same thing.
http://www.knitpicks.com/content/index.php/cat/casting-on/

Put the new sts on the right needle where your yarn is.