Hmm If u want to create,u can just draw something and put in Photoshop.If u want to edit pictures u also need Photoshop or Gimp or whatever program to edit pictures,
First step is sketching a line art to do on PC you'd need a tabled, otherwise pencil + paper. Then you scan it and put it in a program; Photoshop, Paint Tool Sai, etc and do the line art, then you "Ink" or "Colour" it.