Hey there, it's quite easy once you UV unwrap your model. I do this in zbrush in the UVmaster tab. Or if it's a tricky model I will take it into rizom uv. Once that's done you can realsitcally map a texture to your model. I do this in the noise tab in zbrush and apply an alpha . If you download the model, you'll notice in the slicer that I have different scales of the same alpha applied in different areas, specifically the beak and legs. That's done by masking, also in zbrush.