Your trouble is that iTunes is there to manage your files but you're messing with them in Finder.
It's like putting something in a cupboard so you can store it and know where it is, just for someone to come along and move it.
It's pretty straightforward:
Name your files however you like.
Add your files to iTunes
If you can't see them immediately look in the recently added playlist.
Select one or more of the files, right-click 'get info'
From here you are editing the mp3 tag, the metadata.
You can add all sorts of info here. album name, artist, genre, notes, artwork etc.
But once the file is in iTunes you should only ever manipulate it from within iTunes.