They're assuming you're right-handed and I'll assume you're making the smallest size.
If I'm reading that right, you'd start the row with 33 stitches. If you cast off four, which should leave a loop on your right needle, then work three more in whatever pattern you have going, you'll have four stitches on your right needle and you'll be ready to work the rest of the row as written. I counted it a couple of times and got the total they have for the end of the row, but knowing my ability to miscount things, keep an eye on it
I have no idea why they used "when there are four stitches on your right needle" as an instruction--I've never seen it written that way before.