iTunes music audio files and playlist issues

I just logged into iTunes on my Mac Mini after being only on my cell & iPad for a while...

I not that not only are there many (all) playlists missing but the only audio files I can find in the programs lists of songs are one's that I purchased on line... none that I was given... no original audio files / recordings and none of the playlists that still exist in my cell phone and iPAD

Why did this happen? I did not ask for or choose this.. I want all of them back... How can I do this??