I watched the tutorial, the original tutorial was about water pipes. Let me change it:
Rendering:

practice:
1. New file 666x666
2. Draw a small square rainbow fill in the upper left corner of the new layer (not too high) and deselect it.

3. Draw a path from the center of the rainbow image

4. Select the Fingertip (Smudge) tool

Use this for the pen tip shape

5. Adjust the pen tip to a small size and cover the center of the rainbow image.

6. Return to the pen tool, right-click and select Fingertip (Smear)

Got this:

7. Crop it, add some perspective and add a background


Extended effect:


Here’s how:
1. Change the rainbow fill to this and make basic light and shade:

2. Use this tip shape for the smudge tool in step 4 above:

3. Draw the path in the same way as in the tutorial above. Remove the unnecessary parts and you get this:

4. Create a new layer, use a path to draw an arrow, and fill it with the same gradient:

5. Join the arrows, merge the layers, paint the seams, and add some perspective:

6. Layer style color override:


7. Create light and dark effects:
Load pattern selection

Add a new layer gradient fill (left and right)

Mode changed to Overlay (Overlay = Overlay)

8. Make another light and dark effect:
New layer gradient fill (top and bottom)

Change the mode to solid light and adjust the opacity...
