I’m new and I just chose a theme, it had an example that looked awesome. But on my blog it looks nothing like it.
How can I have my blog look like the example, with the changing header picture and the picture slider to go to previous posts?
You might want to look into Triton Lite, a theme just recently added here that has a top post slider similar to that on modularity. Also look at Oxygen and Fresh & Clean, which have post sliders as well.
For premium themes, take a look at Debut or Photography.