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.

It’s called the loop cast on here, but it’s the same thing.

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