In this discussion, I’m going to assume a familiarity with the water bomb base.
(If you’re unfamiliar with the concept of origami bases, start with the origami terms page here.)
Starting with the water bomb base:
Flap one:
1: Squash fold the flap. 2: Petal fold. 3: Fold the flap back down. 4: Book-fold in half.
Flap two
Double-rabbit-ear the flap.
Turn the model over (not shown).
Flap three
1 Rabbit-ear the flap. 2 Open unsink one layer from inside the rabbit-ear. 3 Book-fold in half.
Flap four
1 Reverse-fold the flap downward. 2 Reverse-fold the front and back layers of this flap.
The final result for each flap is the same; we have constructed the frog base from the water bomb base.
