What you need:
Albrecht Dürer Magnus in ultramarine 120, deep scarlet red 219 and warm grey V 274, Water Brush, Watercolour paper with fine surface in DIN A4
Tear a piece of college paper and place the paper before you on the table. Illuminate the paper so that it throws shadows (e.g. with a table lamp). Draw the contours of the paper on the watercolor paper with warmgrey V 274. Where the paper does not lie flat on the ground and throws shadows, add more colour pigments.
Blend the pigments with the water brush. You may use a lot of water. But please make sure that the outlines of the piece of paper remain visible. As soon as the watercolour paper is dry, draw lines with ultramarine 120.
Enhance the shadows with warm grey V 274. Blend the pigments with the wet brush. As soon as the watercolour paper is dry, draw a vertical line with deep scarlet red 219.