Let’s look at the renderings first:
Create a new background layer and fill it with gray, create a new layer, use the pen tool to outline the hairline, fill it with the hair background color, and make it feathery.
Customize the brush, draw the hair in two layers, use the smudge tool to apply, deepen and dodge to draw light and shade. Add shading separately.
Create several new layers and use the same method to draw branched hair respectively, darken and dodge.
Use the pen tool to draw the direction of the hair and stroke it.
Finally, use the smudge tool to modify and merge the layers. Completed.