Blue can be a bit tricky as there are sooooo many variations in color and temperature. For shadows and to push something back in your painting, you usually use a cool blue. Warm blues for sunny skies. It really depends on the color around it and each painting.
The complement is orange. Orange mixed into blue dulls the blue toward gray. Put blue and orange beside eachother and the colors vibrate.
I put "color" in my search box on the left and pulled up these posts about color, value and painting. A good review!
You can put Instruction or other key words and find more posts in the "how to" genre.
Tomorrow will be our GREEN lesson. I'll show you my practice after class. It is so good for me to get together with other artists. You should try it sometime.