As I am only reading the pattern and not making this item it is a bit hard to visualize, but if I am reading correctly, after the first 28 rows you have a square.
The next set of directions have you now making a triangle on top of your square. This occurs because you knit 1 fewer stitch each row, then turn the work and come back (this is called short rows). Each right side worked row decreases till you get to the last which has only 2 worked stitches. However, you still have all 14 stitches on your needle after the completion of each wrong side row. Your needle will now slant in comparison to the original square.
At this point, you work rows, increasing one stitch each time and essentially make a triangle in reverse. You should be "square" again at the end of this.
Check out this short row video. Notice the slant?
Hope this helps.