Help shaping shoulders

I’ve come to the end of knitting the back section of a cardigan. I don’t understand how I’m supposed to finish if somebody could spell it out to me, that would be great.

These are the instructions I don’t understand:

Shape shoulders and back neck
Cast off 5 [6:7:9:10] sts at beg of next 2 rows.
47 [51: 57: 61: 69] sts.
Next row (RS): Cast off 5 [6: 7: 9: 10] sts, K until there are 9 [10: 11: 11: 13] sts on right needle and turn, leaving rem sts on holder. Work each side of neck separately.
Cast off 3 sts at beg of next row.
Cast off rem 6 [7: 8: 8: 10] sts.
With RS facing, slip centre 19 [19: 21: 21: 23] sts onto a holder, rejoin yarn and K to end.
Complete to match rst side, reversing shapings.

It’s the “tyburn” by Sarah Hatton, using rowan big wool. I’m knitting an XL size.

For your size:
Cast off 9sts at beg of next 2 rows. Cast off 9sts at the beginning of the row, work to the end, turn, cast off 9 sts at the beg of the next row and work to the end.
61 sts remain.

Next row (RS): Cast off 9 sts, K until there are 11sts on right needle and turn, leaving rem sts on holder. Work each side of neck separately. You’re only going to be working on one shoulder at a time here
Cast off 3 sts at beg of next row.
Cast off rem 8sts.

With RS facing, slip centre 21 sts onto a holder, rejoin yarn and K to end. Now you’re going to shape the 2nd shoulder in the same way as the first, with cast offs at the armhole edge.

Thank-you. I’ve not been knitting long so perhaps I’m not familiar with some terms.

With 61 stitches remaining, I’ve cast off 9 stitches at beg of next row, then k 10 more stitches so there are 11 stitches on my right needle. Then I turned my work as if I’d finished the row, then I cast off first 3 of the 11 stitches, finished that mini row and then cast off the last 8 stitches.

Now I have 1 stitch on the right needle, am I to cut the wool and knot this last stitch?

If so, I’ve then put the next 21 stitches on a holder and have 20 stitches on left needle. Do I then knit til last 9 stitches, cast 9 off, then cast off 3 on next row, purl til end and then cast off the last 8 stitches? Is that right?

Then what do I do with the stitches on the holder? Cast off straight away?

Thank-you so much!

You’re doing very well so far. There are some good glossaries online including a nice one here with videos. And of course, you’re always welcome to ask in the forum.
Yes, you have the first shoulder correct. With one last stitch left, cut the yarn leaving about a 6 inch tail to weave in later. Then you can simply pull the end through the last stitch (fasten off). See the end of this video:
http://www.lionbrand.com/how-to-knit-binding-off

For the second shoulder, Knit to the end of the row, turn, cast off 9 sts at the beginning of the row. You can really only cast off at the beg of a row; otherwise the yarn becomes isolated at the end of the cast off. Finish the row, then cast off 3 on the next row (neck edge) finish the row, turn and cast off remaining sts. Fasten off the last stitch as above.

Thank-you so much, that’s so helpful. One last question! What do I do with the remaining 21 middle stitches on a holder, do I cast them off too? Or keep them on a holder for the making up?

Yes, the center back sts become part of the collar. You’ll knit across them when you get to the last section on Front band under Making Up.