New Mbr - Sweater Pattern Help

I i’m new to this site so i hope i am posting my question in the correct place …if not please forgive me…I am making my first sweater…I did great until I got to the shoulder and neck shaping which is a turtle neck sweater the pattern says

Cast off 12 sts beg of next 2 rows. Leave rem 30 sts on a st holder.
Does that mean i cast off 12 sts put 30 sts on a holder, cut yarn and rejoin yarn and then cast of the other 12 sts? I need help lol I’m so confused. Any help would be greatly appriecated. Thank you in advance. Terri

You can’t cast off at the end of a row, so you always do it at the beginning.

Cast off at the beginning of the first row, and finish the row. Then cast off at the beginning of the next row and put the remaining stitches on the holder.

Yes, the cast offs are a row apart, but it makes no difference in the end. All sweaters are made this way.