First, fold the square pairs into triangles.

Fold in half along the middle of the triangle to form a smaller triangle, as shown in the figure.

Fold it in half again to make a smaller triangle.

Fold it in half again along the middle and fold it into the shape as shown in the figure.

Use scissors, cut into the pattern as shown in the figure, open it after cutting, and a beautiful window grillage will be ready, beautiful!