How do you play a song from your iTunes library without having the original song on your computer?

On my iTunes library, whenever I add a song to it, it will play it, but whenever I delete the song from where I dragged it from, it will say "The song ______ could not be used because the original file could not be found. Would you like to locate it?" How can I play songs from my library without having to keep every song I want to play? My friend's computer lets him keep songs in his iTunes library and play it without having to keep the original songs. Thank you very much!How do you play a song from your iTunes library without having the original song on your computer?
As far as I know, you can not do this. You generally can't play sound files that you don't have. Also, iTunes is just a music player. It plays music that is found on your computer, it doesn't store it.

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