If you're paying for Apple Music you already get access to every single song in their catalog (like 40 million songs?) and can download them to your device. H

If you're paying for Apple Music you already get access to every single song in their catalog (like 40 million songs?) and can download them to your device. However it goes away once you stop paying your monthly fee. If you want a bunch of songs or albums you don't have it's just a matter of search for it and listening to it, and to hit the 'make songs available offline' button.