It seems to me that it means to put the first 5 sts and the last 5 sts on holders for armholes. That's how I understand it.
So, if I were doing this row, I would place 5 sts on a holder, then knit to the last 5st, put last 5 sts on another holder. Then continue with the next row.
The instructions are dec 1 stitch at neck edge...on alt rows AND AT THE SAME TIME cast off stitches at beg of 2nd row. I am confused between alternating