iTunes and Apple Music library synchronization on Mac and PC

Hi All,

I have two questions here and I'll try to write them the best I can.

1st, I been using iTunes as my main audio source for like ever. I'm also a Windows guy first and it will always be my number one. I use Mac for work. Recently I started using the Apple Music app on my Mac. I noticed when I signed into my id on my Mac I was able to see my entire library which I loaded into iTunes if you will on my PC. I was using iTunes before I knew about Apple Music. How did my files magically appear in Apple Music on my Mac? I'm still getting familiar with Music.

2nd, I installed Apple Music on my PC, now along side iTunes on the same machine. Without being signed into my account in Music, all my stuff is now showing being available only in Music and no longer in iTunes? Not sure what happened there? Is iTunes being fazed out?

Hope that is clear and thanks all.

[Re-Titled by Moderator]