itunes
When I drag music into iTunes from the downloads folder, and then empty my downloads folder, the music is obviously no longer in iTunes because the source file was in my downloads folder.
This is on Windows 7, but I don't think that's relevant. I think it's an iTunes setting/preference.
How do I set it up so when I drag music into iTunes, it copies the music file to another folder, so I can empty my downloads folder?
In iTunes > Preferences > Advanced
Uncheck Keep iTunes Media folder organised and Copy Files to iTunes Media folder when adding to Library
Screen shot provided by @Wheat Williams:
Yes - unless there is something wrong with iTunes and it didn't copy the song, you can delete these second copies of songs.
I would use spotlight to check before you delete things until you gain confidence that the copy is working as designed. In the long run, it will be faster to let iTunes move the files so you don't need to clean things up.
Also, a good Time Machine backup can help if you accidentally delete too much.
Best Answer
Launch iTunes then open Preferences, either from the Edit menu or by holding Ctrl ⌃ ,
In the Advanced tab, check 'Copy files to iTunes Media folder...'
This may prompt iTunes to ask if you want to Consolidate existing files. If it does, say Yes.
If not, then do it manually afterwards, from File > Library > Organise Library.
This will grab all existing files from all locations except the iTunes Library & copy them there.