nope, just makes them available via the Play Music app. You stream them to the phone. If you want the MP3 file you need to download the Google Play/Music Manager programme to you computer. You'll then be able to download the files as many times as you like and do what you want with them.
works perfectly for me as I have unlimited data, so can stream my whole music library whenever I want where ever I want (so long as I have signal, which is basically everywhere these days)