Knowing how to use the pen tool in illustrator is like knowing how to write with a pen. This is the basis of Illustrator since it is a Vector image and these are made up of lines.. Using the pen tool in the background.

Creating Different paths  for the highlights, shadows and mid tones.

Illustrator Shortcuts :

PenTool : P

PenTool ADD : +

PenTool Subtract : –

Select Anchor : A

Group : CMD/Ctrl + G