I have searched the forum and google and can't find a clear answer. Can I use Apple Music or music from iTunes on my slide show? I know in ProShow we could use our own music.
Yes you can; that's what I use in all my slideshows.
However, you cannot import music from Apple Music directly as Apple Music only allows streaming. I buy the album in iTunes Store, download song files (they come in .aac format) and then import them into the show.
Beware that for copyright reasons, you are not entitled neither to distribute your slideshow with that music nor to upload it to a sharing Web service.