It means to draw a diagram. A picture that has words labeling the different parts. Here is an example: http://www.exploringnature.org/graphics/mammals/manatee_diagram.jpg

It means that having drawn the pictures, you will lable the different parts. Meaning, you affix/assign/put names to various parts of the picture. Example: you draw a picture of the human body, then draw arrows labelling the different parts. So, you would have an arrow pointing to the head saying ''head' ....etc