Cast off for armholes

So I’ve watched a few of the decreasing/increasing and casting off videos. I’m not sure which one pertains to what I need though.

I’m working on the back of a baby sweater and I’m now to the point where I shape the armholes. I’ve just finished purling a row.

Instructions say…

[B]Cast off 6 sts beg next 2 rows, 49 sts.[/B]

So if this is one of the decreasing videos, which one do I follow? Or any of the other videos which one?

I’m just not sure what casting off 6 stitches means. Other then I know it’s supposed to make it smaller.

Thanks for any help!
Cat

Cast off means bind off (it’s the British knitting term for it), so BO 6 sts like you do when you’re done with a piece, then work the rest of the row. Doing this on 2 consecutive rows makes the underarm on both sides.

Thanks again Sue!