All the instructions are doing is telling you at the completion of row 8 how many stitches should be on your needle and how many ridges of garter stitch you have worked (garter stitch ridges are equivalent to two rows of work) ie. how much progress you have made and what it should look like. So, after glancing at the pattern you should have increased from 31 or 35 cast on stitches to 51 or 55 stitches depending on what size you are making and have worked/completed 4 sets of garter stitch ridges. I hope I have not confused you even more. The pattern looks cute, good luck and I hope it works out for you.
PS. to increase they want you to knit in the front and back of the stitch they are referring to (Amy shows you how to do this in the Glossary section) and to make 1 simply bring the yarn to the front and knit the following stitch as usual.