Mitten knitting

I have difficulty with knitting the thumb opening of my first mitten. The pattern indicate the following: knit 1 edge st, k1, slip next 13 sts onto a piece of waste yarn, (I’m ok up to here) than cast on 13 sts in pattern, what does that mean. I tried to cast on but it does not look right.

Help anybody.

Hmmm. That doesn’t sound right. The 13 stitches that are on the waste yarn are the thumb, and at that point a pattern might have you finish the row (or round) in pattern, and then cast on a couple of stitches above where the thumb is.
Where is the pattern from?