Okay, so you are indoors, taking a snapshot of a loved one and when you see the result, it looks something like this:
Huh? what the? It was NOT that dark in the room. Why are my subjects totally underexposed? This was a shot taken of my dd with her teacher on parent/teacher conference day, taken with my point and shoot camera. I knew right away what the problem was. It was that huge, sunny window behind them. Here is what happened, and how to fix it!
1. Move your subjects away from the window. You could move so the window is behind YOU, or just move your subjects away from the window completely.
2. Use your flash to fill in the light.
3. Take your light reading from another spot. This is the simplest way to fix this problem - you can do it immediately and results are instant - without moving you or your subject. Okay, so once I saw that my image went way too dark, I simply shifted to my left slightly and pressed the shutter button down half way to focus and take my light reading from the side of the subjects which was darker. I know this might sound confusing, so here is a pic to show the angle I was aiming when I focused this time:
I did this second shot in seconds, and since I told my camera "HERE is where I want you to take the light reading, so make THIS spot the correct exposure" I ended up a picture that looked like this:
Much, much better. I didn't edit this at all, so it's not very sharp for web - but you get the idea. Just from changing where I focused my shot (and, therefore, where I took my light reading) I forced my camera to brighten up the area of the shot that I wanted bright. Yes, it over-exposed the window in the process, but i don't care if the window is super bright as long as my subjects are well lit.
I hope this helps with a very common problem!