That's awesome! I'd recommend all first-step beginners check out Ableton's Learning Music[0] and Learning Synths[1] resources to start. They're both great sites for getting to grips with the basics, and should take ~2 hours each. They're also super accessible, anyone aged middle-school or older should be able to get something valuable from these guides. Learning Synths is particularly salient because it teaches subtractive synthesis, so (almost) all of the parameters it shows you how to use will also exist on the Prologue.
After that, it's mostly up to you. There are hundreds of niches in both sound design and music theory, all of them with their own unique quirks to learn. Let your sense of curiosity guide you, and you'll definitely find something interesting. You should probably look into getting some DAW software if you want to compose full tracks, and a DAC would allow you to record off the Prologue into your computer. It really is an open-ended hobby besides that.
The only other piece of advice I like to give is to temper your expectations. The process of learning music theory and sound design is long, and everyone makes a lot of garbage when they're starting (much like programming). Unlike programming, I find the process of sound design to be pretty therapeutic, and many nights I'd find myself sitting in front of my modular rack instead of watching TV or playing games with friends. Everyone's relationship with it will be a little different, but nobody should be overly critical of their own work. Do whatever is fun to you, and let the inspiration follow.
[0] https://learningmusic.ableton.com/
[1] https://learningsynths.ableton.com/