Then, yes, you can get an app that will play MP3 files. You can copy files to the Android phone the same way you would to an MP3 player. I think you have to put them in the Music folder, but that’s easy.
If you want to spend money (and I know how you love to spend money) I think Google sells an unlimited streaming music service. I have no idea how much it costs. And, of course, if you have an unlimited data plan you can get the i heart radio app or something similar to stream music directly from the Internet.
It looks like T-Mobil has free music streaming and downloads with Smmple Choice plans (which are not free, but, well, you know).