I just finished lesson 3 of the beginner course. It recommends learning a song as part of your daily practice. How do I choose one suitable for a beginner? How do I learn it? I'm not even sure if I'm a soprano or alto. 

Hi, Melissa! Great question.

I walk through how to find your range in this article: https://www.30daysinger.com/blog/finding-your-vocal-range. 

You can look up lists of "easy pop songs for beginning singers" (or replace pop with the genre you enjoy the most). Or you can try singing along with a song you already know (on a playlist, on the radio, etc) and notice if you're able to match pitch throughout the song without straining. If range is a concern, you can narrow your search to "songs with a limited range for beginners", or something like that. Once you've chosen a song, the process of learning it is simply listening and eventually singing along with the original, until you know the melody well enough to sing by yourself with an instrumental/karaoke track (easily found online for free). 

If you let me know which artists you like, and what your comfortable range is, I can try to help out more!