the exposure rule is for the subject. it doesn't care if you are under a tree.
here is one google result. there are dozens of others.
consider taking a note pad and pencil along on your next adventure. draw four columns on the page. you could lable them -
light/scene condition - leave some room to describe the light on the subject.
aperture - what you believe the aperture setting should be and shot at
shutter - what you believe the shutter speed should be and shot at
result - too dark, too light, just right.
analize your results without doing any corrections. don't even think about judging this on the tiny little screen on the camera. the trick is to record the shadow details and highlight seperation.
good luck, this concept confounds a lot of people.
Forty years of photography.
Fifteen years of training young professional photographers.