I’m not sure it does, or if it does it doesn’t work very well. I have an apple music subscription. If I enable iCloud Music Library it only adds the songs to my other devices if they’re available on Apple Music.

There doesn’t seem to be a way for me to upload my own MP3s to the service like you can on Google Play Music.

No it doesn’t.

It’s a separate service

There's 2 ways Apple handles music you've ripped. If the music's fingerprint matches that of something they already have in the iTunes Store, your iCloud Music Library will be populated with the iTunes Store version of the song, so you can download that on your other devices. Only the original uploading device retains the original file. This is usually a good thing as the iTunes Store version is frequently better-quality than whatever MP3 or AAC you had ripped.

The second way is if the file's fingerprint doesn't match any song in the iTunes Store catalog, then with iTunes Match, iTunes will actually upload the whole file and your other devices will then stream or download that exact file. There are some limits here; I think there's a limit on the song duration (not sure what it is but I'm pretty sure songs over 1 hour are past the limit), and there's a limit on total number of songs (at launch this was 25k; I think they've raised it higher but I don't know what the current limit is). Whatever the limits are, I do know my father's music collection (all manually ripped from a massive CD collection) is too large for iTunes Match, so he's stuck managing music the way we all used to do before Apple Music and iTunes Match came along.

As far as I'm aware, the Apple Music subscription supports the first mechanism but not the second, and the iTunes Match subscription is needed for the second option. That said, I'm not 100% positive.