Sorry I drifted off last night.
Option 1: The *easiest* way is to make sure the preference to let iTunes manage the music is checked. When you do this, iTunes maintains its library inside your Music folder, and it automatically puts music in folders, etc. You really never have to go in there at all, because everything else happens in iTunes (you can view music by genre / artist / album / etc, search, use playlists, etc). If you do it this way, when you're bringing in a file you already have, you drag it into iTunes, iTunes will copy it, and then you can delete the original file.
Option 2: Some people, particularly people who've become accustomed to Winamp on Windows (or to flash players that need you to manually manage song organization), really want to manage the file structure -- what is in what folder, etc -- themselves. You do this by turning that preference to let iTunes manage the library off. In this case, when you drag the song into iTunes, it doesn't copy anything. iTunes makes a note that the file is wherever you dragged it from. When you do this, you don't want to drag from an external media like a flash drive, since iTunes will expect the song to be available on Flash drive whenever it looks for it.
I really recommend the first option. It's much less hassle. If I get a song off a website or something, I save it to my downloads folder or my desktop, drag it into iTunes, and then delete it. Many programs like iRecordMusic can directly dump a song into iTunes. If I want to manipulate a song with another program (e.g. put it in SoundStudio to make an edited ringtone), I just drag it from iTunes to the desktop, which makes a copy, and then I edit the copy and delete it if necessary when I'm done.
Does that help?
