Here's a watercolor from around 1965 by George Post. Because he uses only hard edges it is not difficult to see each of his shapes as a series of layers. Look at the dock in the foreground. Before the middle value shadow and the dark lines between planks were applied the whole shape was given a light layer of a warm neutral. Light first, then middle, then dark. Three layers.
How many layers do you see in the water? What about the red buildings?
Shape by shape, Post's paintings resolve neatly into a sequence of layers that proceed from light to dark and from general to specific. Here's another by the same artist:
Here's a portrait by Mary Whyte:
It's not as easy to see the layers when colors are blended on the paper. Shapes grade from one value to another with soft edges in between. Here's another Mary Whyte painting done more quickly:
Here the different values are easier to locate. The hair, for example, displays white, light gray, dark gray and black.
For homework, translate one of the following photos into a three layer watercolor. Some areas may only require two layers, others may need four. You may find it helpful to work with mostly hard edges, in the George Post style. Have fun