We have a really helpful article here on how to remove duplicates:
How to find and remove duplicate items in your iTunes library
I was also able to find an article about editing and arranging content here:
Playing and managing content in iTunes
Hope those help,
Trying to organize music files from computer into i tunes and remove duplicates, find tags etc basically cleanup
Hold down Shift and then press View > Show Exact Duplicate Items (before releasing shift) as this normally gives a more useful selection of "true" duplicates. You need to manually select all but one of each group to remove. If you have multiple references to the same files then don't send to the recycle bin. Use my DeDuperscript if you're not sure or don't want to do it by hand. See this thread for background and please take note of the warning to backup your library before deduping.
(If you don't see the menu bar press ALT to show it temporarily or CTRL+B to keep it displayed)
For general tips on organizing things in iTunes see Grouping tracks into albums.