Does it have a picture of the pocket on the apron? If it is a St st pocket with k1, p1 ribbing along the top I'd say the whole set of instructions are wrong. It sounds like they give instructions for a whole pocket at the first--knit some St st then some ribbing, that part you had the question about
SI (yes that's definitely an upper case i) sts onto a stitch holder.
seems like it doesn't belong there at all. From the last directions for the pocket all you do is do the St st and then some ribbing. It also sounds to me like that last whole part about how to continue the pocket is redundant because you just knitted 6 rows of ribbing, why add another 6, unless, possibly the edge is folded over.
But I see nothing fancy going on that would require you to slip X number of stitches at the earlier point where it says SI etc. Does it ever tell you to cast off this pocket? Seems like it would be a needed step?
Does it give some finishing directions that involve turning the cuff of the pocket down? A basic patch pocket is usually some St st with a ribbed cuff, cast off. Sew it on. Is the pocket pictured something other than that?