The best way to learn is ( for example ) download a watch face with touch icons . Open up the clock_skin.xml and print it off . Split it up into sections with a ruler and pen . If you look closely at sections some are easy to figure out as to what they do . I used to write down what each section did alongside each section to remember or to copy - paste into new clock skins . Then why not download other faces that interest you and do the same ? For example someone may have created a face with a icon for the camera which opens the camera . Again print of the clock_skin.xml and section of the code .
Lastly just like you did with whatsapp you can insert what you like into your COMPLETED faces that you have made in WFD .
This one is a great example to read through -
Obviously dont use any of the designers images etc ( just read his code ) which he has kindly labelled . Thanks @Odin
Thanks
Andy