Sleeping sack

I’m trying to knit a sleeping sack for my future grandnephew. Now that I have to divide the front opening, it says: Next row (WS) bind off 1 st, work to last st, k1-tbl–111 sts. Next row: Sl 1, work to last st, k1-tbl. Continue working established pat back and forth…
What does this means? Please help!
Thanks
Mannie

First, bind off one stitch, work to the last stitch, then knit one through the back of the loop. Next row, slip one stitch, work to the last stitch and knit through the back of the loop again.

You will not be knitting in the round but knitting flat so you will turn your work and work back and forth as if you were working with straight needles.

Next row (WS) bind off 1 st, work to last st, k1-tbl–111 sts. Next row: Sl 1, work to last st, k1-tbl.

In plainer English:
Next row (wrong side) bind off 1 stitch (so you would knit 2 sts and lift the first of those over the 2nd one and off the end of the needle), now work across the row until you have 1 stitch. Knit that last stitch through the back loop (insert the right needle into the stitch behind the needle, head on rather like you were purling the stitch, but behind the needle, yarn around and pull up your loop). You will now have 111 stitches.

Next row: Slip 1 stitch (move it purlwise to the right needle without working it), work across the row to the last stitch and knit that stitch through the back loop as before.

Continue working established pat back and forth…
If it is written just that way, it should mean to keep working in the same pattern stitch you were before over the slightly decreased number you now have. If that doesn’t make sense from the picture or schematic it may mean to keep decreasing every other row, but I don’t think so. I’d need to see the pattern to be sure. Do you have a link?

Oh, zkimom’s insight is probably right. If you have been knitting in the round, they mean for you to start working flat.