If it is the step 8 of the diagram you are having trouble with, the easiest way for me to do it is fold the paper in half horizontally,the "line folded" should go though the middle of the kite shape. Now notice that the top part of the kite shape (which is the part faces the center point of the paper) is smaller than the bottom part of the kite shape (which faces the outer part of the square) the line made by step 5 should separate the different parts. Now mountain fold the whole perimeter of the kite shape and valley fold the line in the middle.
while collasping valley fold the perimeter of the square made in step 1 and mountain fold the the lines made by step 4 and the perimeter of the kite shape (is the other two one). Mountain fold the middle line on the horizontal axis. NOW WE ARE READY
, valley fold the diagonal made in step one AND mountain fold the vertical line, try to collaspe it like the other two kite shape. Now fold the two iner flaps up and now is a right angle triangle 90 degrees, fold the top point down to the point on the side of the paper, the fold should be 45 degrees. Now you are on step 12, the rest should be easy, good luck