How do I move music from desktop to iTunes on the same computer?

Question

I have new music on my Macbook desktop. I want to move it into iTunes.  This was easy with iTunes 10, but it doesn't work with iTunes 11. So how can I manage new music that isn't purchased throught the iTunes store? How can I move music into iTunes?
I'd really like to go back to iTunes 10 since it was user-friendly and iTunes 11 is extremely iTunes friendly; os if you know how to do that I'd appreciate it greatly.  Or I'd appreciate learnig about another music management system - other than iTunes since iTunes 10 isn't available any more.

Answer 1

=Downgrading from iTunes 11 to iTunes 10.7=
You may be able to go back with Time Machine but this may involve restoring other items too (https://discussions.apple.com/message/20441404).  Alternatively:
Back up your computer first, in case the unexpected happens.
Quit iTunes.
Get iTunes 10.7 from http://support.apple.com/kb/DL1576 or the direct download link at:  http://appldnld.apple.com/iTunes10/041-7195.20120912.d3uzQ/iTunes10.7.dmg
Do a few preparatory steps by making sure all iTunes components are not running and cleaning old files.   See https://discussions.apple.com/message/20475394.  Do steps 3 and 4.  Steps 6-8 may be also useful but I don't know if they are essential.  Some of the other steps are not necessary, duplicate steps listed later in my post or are perhaps even unhelpful in the process.
Replace the iTunes 11 application with iTunes 10.7.  Simply dragging the application to the trash may not work. Lion (OSX 10.7) and newer systems have iTunes integrated into the operating system and deleting is a bit more involved.  Two ways to do this are:
1.  Use the shareware Pacifist utility (http://www.charlessoft.com/) to install iTunes 10.7 including all associated system files. Details at http://forums.macrumors.com/showpost.php?p=16400819&postcount=6
2. Check this reference on how to delete the iTunes application itself:
    Delete iTunes in Mac OS X 10.7 Lion - http://osxdaily.com/2011/09/13/delete-itunes-in-mac-os-x-10-7-lion/
    After deleting the application there may be other files that need downgrading too. See the note about error -42408 at the end of this post. You may want to tuck these away somewhere safe until you have completed the installation of iTunes 10.7.  I have not tested this but ideally if newer versions are not found then the installer will put in the old versions. This may include these files in /System/Library/PrivateFrameworks/ which apparently get updated by iTunes 11:
AirTrafficHost.framework
CoreFP.framework
DeviceLink.framework
iTunesAccess.framework
MobileDevice.framework
After doing one of the two procedures above you will have to rescue the most recent old iTunes library from your iTunes > Previous Libraries folder. Rename it "iTunes Library.itl"  and replace the existing one in the iTunes folder. A newer version of iTunes irreversibly updates your library file so you have to replace it with the old one or you will get an error message. Note, this will revert your library to the version at the time of the upgrade and you will have to update any changes made since.  See:
https://discussions.apple.com/message/20401436 - turingtest2 11/2012 post on rebuilding empty/corrupt library from previous iTunes library file after upgrade/crash.
iTunes: How to re-create your iTunes library and playlists - http://support.apple.com/kb/ht1451
Other issues:
- https://discussions.apple.com/message/20432309 - solution to mobile devices saying they need to be restored after downgrading
- If you encounter error -42408:
iTunes: Advanced iTunes Store troubleshooting - http://support.apple.com/kb/TS3297 > Specific Conditions and Alert Messages: (Mac OS X / Windows) - including specific error codes.
Alternatively, check https://discussions.apple.com/message/20441424 which requires you have a Time Machine backup (though possibly if you remove the newer version of these files old ones may be installed with the iTunes 10.7 installer - untested).  A  variant of this is at: https://discussions.apple.com/message/20448184
- Persistent "Show in iTunes Store" arrows after downgrade - https://discussions.apple.com/thread/4567064