How to import music from the hard-drive into iTunes?

I got a new computer and downloaded iTunes. Of course now I need to transfer all my iTunes content (that is on my iPhone) on to iTunes on the new computer. I tried syncios and iExplorer and they both save the music to a file in the computer hard drive. Supposedly these programs can transfer the contents of your iPhone into iTunes but I don't understand how if it is now saved in a file. Is there a way to import music from this file into iTunes? Everyone has been telling me to use this software but i don't know how.

thank you times a million

Added (1). Clarification--- when you all say drag/copy the files into itunes, does that mean the itunes itself (like when the program is open) or the itunes file in the programs menu?

You sync your phone with your computer in Itunes and backup it will back up your whole phone including your music

You should import first your musics files from your computer to iTunes, this could be done by drag and drop method, select all your music files and drag it and drop to iTunes, After you see that your musics is on iTunes you can now import it from iTunes to your iPhone by connecting your iPhone to your computer and access it from iTunes select a music library and drag all music you want to transfer to your iPhone.