Here are a few useful questions related to value;
What is the lightest thing in the picture? What is the darkest? Working from light to dark, what would you do first? When do the light shapes get their definition?
The relative lightness and darkness of the shapes is where the feeling of light in a scene resides. These relationships are observed entirely by eye. What your brain tells you, like that this is a white house, can get you into trouble. This is a white house but it is not white in the photo. Better to ask something like, "Which is darker, the house or the sky?"
How dark is the house?
Anytime you ask how dark something is, the answer is always the same, "Compared to what?"
The house is lighter than________, but darker than________.
For homework, most of you brought home a picture from class. Using those or one of the above images, try breaking the scene down into three or four layers according to value. Keep it very simple. The object here is to get used to thinking a couple of layers ahead of yourself. We are not making handsome paintings today.
But, have fun!