The short answer would be look at
Gerwin's Crease Pattern Guide, but I'm in a good mood so I decided to make a photo tutorial just for you.
First you need to precrease the paper into 24ths and add the diagonals as shown in the CP.
Fold the paper in half.
Inside reverse fold the upper corners.
Open one side and open sink a square like shown, allowing the attached paper to fold flat.
Fold the new created flaps to the right and repeat on the other side.
It should look like this.
Now look at it from the side.
It's possible to lay it flat down. Looks like a house, eh? Concentrate on the roof. It consists of three waterbomb bases next to each other. Open sink the first one in and out on existing creases.
Like this.
Repeat on the next one.
And on the last one.
Done. Now we'll concentrate on the left side of the house. Collapse along the diagonals to get additional waterbomb bases.
They'll go into the model.
Arrange them evenly. This is how it looks from the side.
And this is how it looks from below.
For the next steps it's advisable to flatten the paper underneath a little bit, but do not unfold it completely.
Open sink one of the new waterbomb bases in and out on existing creases.
Repeat with the other two.
Now flatten the paper between two of these sunken waterbomb bases and valley fold the paper between them up in half.
Like this.
Repeat on the second connection.
Fold the side flaps up as well. Afterwards rotate the model so that the part we just worked with is now on the bottom.
Now you need to fold waterbomb bases with the remaining paper that sticks up on top.
Arranging the paper is a bit tougher on this one.
Slightly open up one of the new created waterbomb bases and sink it in and out on existing creases.
Repeat on the next one.
And finally on the last one.
It should look like this.
Like before we need to flatten the paper between the bases and fold the flaps hidden there up in half.
First one done.
Second one opened up.
And folded upwards.
The side flaps need to be folded upwards as well.
This is the finished base, it folds flat.
This is how it looks from above.
This is how it looks from below.
And this is how it looks from the side.
Have fun with shaping!