''Making'' peds is basically beyond my perspective. However, once uppon a time, i do edit some.
Editing means, editting an existing TXD file. In a TXD file you can find pictures of the face, pants etc. depending on how the maker of the mod did things. When you look at these images you have to find out yourself which are the pants etc. Which wont be too hard most likely. After that, you export the PNG file / JPG file and start editing it. When importing it again, make sure the file is not compresed : Properties of file > Compressed DXT > Off. Then you import it on the old image file ( in the TXD file ). After that you're basically done editing a TXD file.
Cheers, Salmonella