Increase on both sides of established stitches

I have 15 stitches on my cable needle now. I’m now supposed to cast on 24 stitches on each side of the established 15 stitches. I’m not sure how to do this. Then when I do cast on the stitches is that considered a row or not? Thanks for any help in advance.

Use the knit or cable cast on at the beginning of the row. Instead of a slip knot, start with the first or first 2 sts on the left needle. Cast on 24, that just casting on, then when you knit across them you continue knitting on the existing sts, and that will be a row. Then turn and cast on another 24 sts, work across them and the existing sts.

That was so easy and makes sense now. Thank you so much.