Step 1:
This is a complete white paper.
Valley-fold over this line.

Step 6:
Prefold in half over this line.

Step 5:
Valley-fold over this line.

Step 2:
Prefold in half over this line.

Step 4:
Prefold the edge to the prefolded line.
Then, unfold the model.

Step 3:
Prefold the edges to the centerline.

Step 10:
Valley-fold over this prefolded line.

Step 8:
Make sharp folding lines over the purple parts.

Step 9:
Make sharp folding lines over the purple parts.
Then unfold the model.

Step 7:
Valley-fold the edges to the centerline.

Step 16:
Draw two red lines on the model.

Step 15:
Fold over these two lines. The line below is already prefolded.

Step 12:
Turn the model.

Step 11:
Prefold over these lines, use the prefolded lines as guidance.

Step 14:
Prefold over these lines, use the prefolded lines of step 13 as guidance.

Step 13:
Prefold over the short purple lines, they are in the center of the prefolded lines.

Step 21:
Make an inside reverse fold on four places. Not all three lines are visible on the left (just one).
And mountain-fold over the line on the right.

Step 19:
Glue or tape the edges indicated by the two pairs of purple lines together

Step 20:
Do the same as in step 19 on these two places.

Step 18:
Repeat step 17 three more times.
And mountain-fold over the two lines on the right.

Step 17:
Tape or glue the edges indicated by the two purple lines together.

Step 22:
Tape/glue these edges together.

Step 28:
Press the edge on the right over the edge on the left.

Step 25:
Tape/glue these two edges together.

Step 26:
The model is rotated a little to the left here.
Tape/glue these two edges together.

Step 24:
Tape/glue these two parts together.

Step 23:
Turn the model.

Step 29:
Repeat step 28 three more times.
Finally, glue or tape the edges together.

Step 27:
Make sharper folding lines on the four corners.