What you are paying for with an Apple Music subscription is the right to play just about any music you want to play from a nearly unlimited (100+ million song) catalog. Ad-free, in any order – but only for so long as you subscribe.
Apple Music - Apple
When you purchase music (on a CD, or from the iTunes Store), there's no ongoing subscription fee, but you're only getting one particular album, song, or box set.
E.g., here's an album that I imported from one of my CDs.

A search shows that the Apple Music subscription catalog contains a similar album. (I am a subscriber, so if I hit "Play", the Music application would play entire songs.)

I can also go to the iTunes Store, where an electronic version of the album is for sale for $12.99 USD. (Note the "$12.99 Buy" button under the album art thumbnail.)

Buy music from the iTunes Store on your Mac - Apple Support