If you go back through the outdoor portraits you've taken on sunny days, you'll probably notice
that in some of them the subject's faces are very dark, but the background is exposed properly, like in this photo of Mindy to the right. That's a problem because the whole point of the photo was to
show the people! You probably didn't even notice it before, but now it's going to bug you every time you see it. :)
There are many ways to solve this problem, but in the name of simplicity I am going to show you one solution now and some others at later dates. Here goes:
1) Review your image and check to see if the faces are darker than you would like.
2) If the faces are too dark, find the button that looks something like "+/-". It is called exposure
compensation and it might be a button on your camera, but it is likely a menu item you need to
find. When you have found the "+/-" button, move the marker from 0 to +2. (If +2 is too bright, knock it down until the face is exposed correctly).
Boring Details:
You may have noticed, if you are a careful reader that the solution for portraits in the sun is exactly the same as the solution for pictures in the snow! The reason is that our cameras aren't quite smart enough to know how to expose everything in every situation properly and there are a few situations that will routinely trick your camera into underexposing your image.
In this case, the camera was looking at the big picture and saw that the majority of this picture included very bright objects behind Mindy. So it did the best job it could to properly expose as much of the picture as it could.
Keep in mind every situation is different, so just experiment with your exposure until you get something that looks okay to you. As a matter of fact, in the final image of Mindy, I didn't move the marker to "+2" like I recommend in the tutorial. I only moved it to +1 2/3, because proper exposure it not about the numbers, but about what looks good to the photographer!
If you look at your old pictures again... (you know, the one's with underexposed faces), you will notice that they are probably all on sunny days when the sun is BEHIND your subject. You've probably heard the rule of thumb to keep the sun over your shoulder when you are taking pictures. In other words, keep the sun IN FRONT of your subject. That will certainly eliminate this problem of underexposing your subject, but it can create problems of it's own: squinting, boring flat light.
As a general rule (that I break all the time), when I am shooting portraits in the sun, I keep the sun behind my subjects and just expose for their faces. Yes, I blow out (overexpose) the background to a degree, but I like that look, so I am okay with the trade off.