The other day I was watching the sun rise over the lake in Chicago. It was a beautiful sight and while I was taking photos of the buildings reflecting the beautiful orange light, most of the people around me were lining their friends up in front of the sunrise and taking their photos.
There are thousands of people who do this every day, but unfortunately I think most of their photos will come out darker than they wanted. The problem is that, with their backs to a strong light source, the side of their body that face the camera is entirely in shadow. Also, the strong light source overwhelms the camera and it darkens the whole photo down to compensate, which makes those shadows even darker.
The fix? The easiest way to fix this is to turn the flash on and use fill flash to brighten your friends up to match the brightness of the sun in the background. With an advanced camera you'll have something called "exposure compensation", which is just a fancy way of saying that you can brighten or darken the photo yourself. This is the other way to fix this issue -just set the brightness up somewhere between "+1" and "+2". That should help as well.