2. With the "Polygonal Lasso" tool draw a shape where you want to have the crease

3. Create a new layer above the paper and select the "Gradient" tool and choose linear gradient, then draw the gradient starting from the lower left of the selection and move towards the center

4. Use the "Polygonal Lasso" tool again to draw another shape on the opposite side

5. You will notice that the white space of the previous selection is next to the dark space of this selection: this is exactly how the crease will magically form!

6. At this point change the blending mode to "soft light" and the opacity of 12% (these are the values I have set but you can put the ones you like) in this way you will make everything even more realistic

NOTE: You can "play" to make as many lines as you want but just remember that the light side of a gradient must be directly adjacent to the dark side of the other because ONLY in this way a crease can be obtained.

Good fun 😃