I'm not very sure if it's called "main noun" (sorry, I didn't pay attention in my grammar class). But anyway, here's an example:
I decided to start my search at the library. Why? Well, it had more reliable information than the Internet -- than a bunch of blogs, tabloids, and news sites.
The library, that's where I decided to start my search. Why? Well, it had more reliable information than the Internet -- than a bunch of blogs, tabloids, and news sites.
The bolded part is what I call the "main noun" (the main focus of the sentence).
How do you decide its position?
How does the meaning differ in my two examples?