You are also making two pieces that will then be joined. I don’t know why they refer to an “M” as though there were two colors. I don’t see anywhere where it tells you to use any other color. Anyway…
This first part is made in the M color; it starts with 32 sts and ends with 22 on a holder. Cut the yarn when you finish it.
Cast on 32 sts
make button hole - k2 ynfwd k2 tog k to end
(wrong side facing) cast of 10 sts, k to end
k 6 rows
break of M and leave on a holder
Then you start the second piece.
cast on 6 sts
k 10 rows
break of m and leave on holder
So cast on the 6 sts and work 10 rows leaving the 6 on the holder, cut the yarn.
Now the part you don’t get…
with right side of work facing rejoin M and pick up and k6 sts up right hand edge of 6 sts left on holder, k across sts on holder, pick up and k6 sts down left hand edges of these 6 sts and with right side of work facing k across 22 sts on first holder
k 5 rows
Okay, take that little piece that you knit on the 6 sts and hold it in the orientation in which it was knit, in other words hold the cast on edge at the bottom and the sts on the holder at the top, and have the right side up. While you are holding it this way, look to the right side of the rectangle. Turn the rectangle so that that right side is now at the top. Along what is now the top edge pick up and knit 6 stitches along that edge. (If you don’t know how to do this see below.) Now you are at the corner where the 6 sts are on the holder. Knit across those (either off the holder or put them on a needle so you can knit them off). Now you are at another corner, turn and pick up 6 stitches along the other side of the 10 rows across the piece from the first 10 rows where you picked up the 6. Now pick up the first piece you knit, the one with 22 stitches on a holder. (Probably you will want to put those on a needle to work them off, a double point works well for this, as you can access either end. The dpn can be any size from the one you are working on down in size. Another needle will work.) Hold the piece so that it is right side up and so that it is in a position in which you can knit those 22 stitches off onto the needle you are working on that now has 18 sts on it. Knit the 22 onto the needle with the 18.
You may find that it is easier to pick up the 18 sts and then knit on the 22 if you use a few dpns (I don’t know I haven’t tried it) because you are kind of knitting in a tight curve. You don’t have to use the dpns in the round, just work from one needle to the next and then turn back and work the other way, flat. Use just one longer needle if that works.
If you don’t know how to pick up stitches (and pick up and knit is covered here). First there is this from an on-line knitting book LINK The chapter is called “picking up stitches for sleeves” but it covers other applications. Read both pages, the first one is about picking up and the second page covers garter stitch (your situation). This LINK is from this site and has a video about picking up stitches. Scroll down about 3/4 of the page to “Picking Up Stitches”.
I think that about covers it. Hope you find this helpful.