The Diagrams:

1. If you want the colored side out
   start with a square, colored side up.
   Fold a waterbomb base,
   colored side out...
2. ...waterbomb base in progress. Close it up neatly.
3. Valley fold the tip of one flap to the top of the model.
   The crease should run to the midpoint of the lower edge.
4. Unfold to Step 3.
   (Note: Steps 3 and 4 are precreases for the petal fold.)

5. Valley fold the long edge of the flap to the centerline.
6. Unfold to Step 5.
7. Begin the squash fold.
   The flap has two layers.
   Using a finger or chopstick,
   separate the two layers...
8. (Exaggerated 3-D view.)
   ...fold the near layer along the centerline.
   Leave the hidden layer in place.
   The tip will come up and over...

9. ...neatly flatten the layers...
10. Like so.
    Steps 5-9 are called a squash fold,
    because of the "squashing" motion to flatten the layers.
    
    Book fold.
    A book fold is a kind of valley fold: Valley fold one-half of the flap,
    just like turning a page of a book.
11. Bisect the tip, as shown.
12. Unfold to Step 11.

13. Unfold to Step 10.
14. Repeat Steps 10-12 on the left.
15. Note that a white tip is showing. Repeat Steps 10-14 on the other three flaps.

16. Note that the white tips are showing
    and that there are 4 layers on each side.
    Book fold one layer to the right.
17. Like so. Turn over from side-to-side.
18. Note that two white tips are showing,
    and that there are 5 layers on the left side,
    and 3 layers on the right side.
    Book fold one layer to the right.

19. Note that NO white tips are showing,
    and that there are 4 layers on each side.
    Petal fold.
20. Fold the tip back down.
21. Repeat Steps 19-20 on the other three sides.
    Book fold as necessary.
22. The finished frog base.
    The frog base is used in the traditional frog and 4-petalled flower.