To the OP: You need to do research on HDR and look at some example photos (a forum thread may not be enough help). Once you learn what it is, you will LOVE it!
I try to explain it to people like this:
When outside taking pictures, when you focus on the ground, it is clear and easy to see - but the sky may look like a bright, white mess.
If you focus on the sky, you may suddenly see all the blue up there along with white, fluffy clouds. However, the ground is now pitch-black.
Which scenery do you focus on? Which picture do you take? With HDR, you don't have to decide!
HDR takes multiple pictures, focusing on the brightest and darkest spots, adjusting accordingly - it takes a picture where the ground is perfectly visible and it takes a picture where the sky is perfectly visible, and then *combines* them.
You end up with a "perfect" photo where everything is visible, and nothing is washed-out.
I actually purchased an HDR app for my 3GS (iOS 4 & 5 only enable HDR on the 4 and 4S). It worked great, and I ended up with some amazing vacation photos. One was taken on a beach. The ocean, sand, and sky were all clearly visible in one shot.