Start with an origami preliminary base, I have a guide for that so don't worry if you don't know how to make one ;) Arrange it so that the open end is facing you

Take one layer

And squash it flat like this, if this makes no sense to you go to the next steps

Okay again start with the open end facing you

Take a layer

Open it up

Start to squash it

Aline it

And squash it flat

Okay, onto the next layer

Repeat the last few steps

Fold the edges up to meet with the centre

Unfold

Open up

And squash it flat

The completed frog base