Another quite common fold in origami. You’ll see it used in the Bird Base.
1) Start off with a square base.
2) Make a valley fold towards the center on each side.
3) The completed valley folds. Crease the folds well and unfold them.
4) Now make another valley fold across the top along the line.
5) The completed valley fold. Crease this fold well and then unfold it.
6) Now lift up the top flap and fold it back across the crease you just made near the top.
7) As you raise the flap up you want to fold the edges along the creases you made in step 2.
8) This is the end result. Most of the folds should fall in place because of the creases you made earlier. This is the completed Petal Fold.