Step 1:
I used two 5 Euro notes for the skirt.
Prefold them in half over these lines.

Step 8:
Hold the spots indicated by the arrows against each other.

Step 6:
Turn the model

Done!

Step 10:
This is the back of the skirt.
Turn the model

Step 9:
Fold over the line on the right first, then over the line on the left.

Step 5:
Fold over these lines, the mountain-folds are already prefolded.

Step 7:
Mountain-fold on the corners

Step 3:
Valley-fold over the line on the right, then over the line on the left.
Pull the ends on the left outwards.

Step 2:
Prefold the edges to the centerlines.
Then lay the backside of the notes against each other.

Step 4:
Mountain-fold on the corner in the center.